Crash

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Today
The film begins with commentary by passenger Detective Graham Waters (Don Cheadle) having suffered a car accident with his partner Ria (Jennifer Esposito). He mentions that the citizens of Los Angeles have lost their "sense of touch." Ria and the driver of the other car, Kim Lee, exchange racially charged insults. When Waters exits the car, he arrives at a police investigation crime scene concerning the discovery of "a dead kid."
Yesterday
While purchasing a revolver at a gun store, Farhad (Shaun Toub), a Persian shop owner, and his daughter Dorri (Bahar Soomekh), argue in Persian over what box of bullets they should buy. The gun store owner grows impatient and degrades the two of them by referring to Farhad as "Osama". Farhad clarifies that he is an American citizen but the store owner continues exchanging racially stereotypical insults at Farhad and has the security guard escort him out of the store. Dorri demands the store owner to give her the gun or give her back the money. After the store owner gives the gun to Dorri, she asks for "the ones in the red box". The store owner asks why, but Dorri does not answer and insists on buying that particular box. In another part of town, two black men, Anthony (Ludacris) and Peter (Larenz Tate), argue over racial stereotyping of African Americans after Jean Cabot (Sandra Bullock), the wife of the local district attorney Rick Cabot (Brendan Fraser), walks in another direction whilst fearfully staring at them.
Anthony and Peter carjack the married couple as they are about to enter their Lincoln Navigator. Later, at the Cabot house, Hispanic locksmith Daniel Ruiz (Michael PeÃ±a) is changing their locks when Jean notices his tattoos. She loudly complains to Rick about having been carjacked and now having to endure a Hispanic man changing their locks, feeling he will give copies of the keys to "his gang banger friends". Having overheard this, Daniel leaves the keys on Jean's kitchen counter. Detectives Waters and Ria arrive at the scene of a shooting between two drivers. The surviving shooter is a white male, identified as an undercover police officer. The dead shooter, a black male, is revealed also to be an undercover police officer. There is a large amount of cash found in the black officer's trunk. This is the third time the white officer has shot and killed a black man.
LAPD officer John Ryan (Matt Dillon) calls an HMO on behalf of his father and has an argument with a representative named Shaniqua Johnson (Loretta Devine). He then gets into the squad car with his partner Tom Hansen (Ryan Philippe) and sees a car passenger performing fellatio on the driver of a moving vehicle. They pull over the Navigator similar to the one carjacked earlier, despite discrepancies in the descriptions. They order the couple, television director Cameron Thayer (Terrence Howard) and his wife Christine (Thandie Newton), to exit. Cameron is cooperative, but Christine is argumentative. This annoys Hansen, who manually molests Christine under the pretense of administering a pat-down. Intimidated, Cameron says nothing. The couple is released without a citation. Once home, Christine becomes enraged that Cameron did nothing while she was being violated. Cameron insists that what he did was correct and storms out.
Arriving home from work long after dark, Daniel finds his young daughter, Lara (Ashlyn Sanchez), hiding under her bed after hearing a gunshot outside. To comfort her, Daniel gives her an "invisible impenetrable cloak", which makes her feel safe enough to fall asleep in her bed. In the carjacked SUV, Anthony and Peter, arguing and distracted, hit a Korean man while passing a parked white van. They argue about what to do with him, finally dumping him in front of a hospital and driving away. Due to the blood in the vehicle, they are unable to receive payment for the carjacking. The next day, at the Los Angeles Police Department station, Hansen talks to his superior, Lt. Dixon (Keith David), about switching partners. Dixon, a black man, claims that Hansen's charge of Ryan as a racist could cost both Hansen and Dixon their jobs. Dixon suggests a transfer to a one-man car and mockingly tells Hansen that he should justify it by claiming to have uncontrollable flatulence.
Ryan visits Shaniqua and apologizes for the argument. He explains that his father was previously diagnosed with a bladder infection, but he fears it may be prostate cancer. Shaniqua nearly calls security to escort Ryan out of her office when he proceeds to insult Shaniqua by calling her an affirmative action hire. When Ryan asks for his father to see a different doctor, Shaniqua denies the request and he storms out of her office in anger. Meanwhile, Daniel is seen replacing a lock at Farhad's shop and tries to explain to him that the door frame needs to be replaced. Farhad, whose English is limited, misunderstands and accuses Daniel of cheating him, which causes Daniel to leave.
Today
The next morning, Farhad discovers the store has been wrecked and defaced with graffiti. His insurance company does not cover the damage, calling it a case of negligence due to the defective door. When Farhad is told that his shop will be closing down, he vows revenge on Daniel. Detective Waters visits his mother (Beverly Todd), a hard drug abuser. She asks him to find his missing younger brother. He promises and takes notice that there is almost no food in the apartment as he is leaving. When he tries to present evidence in the shooting between undercover police officers, his superiors tell him not to reveal the cash in the black officer's trunk, saying that their work in crafting a non-racist image for the department will be undone.
Jean comes home and sees dishes in the dishwasher. She accosts her Hispanic maid Maria for not putting them in the cupboards. Ryan comes across a car accident and as he crawls into the overturned vehicle, he finds Christine trapped. Upon recognizing Ryan, Christine becomes hysterical, but gasoline is leaking from the tank and running downhill towards another wreck, which has already caught fire. He calms her down, and with the assistance of his partner and spectators, Ryan pulls Christine out just as her car bursts into flames. Anthony and Peter approach another Navigator which happens to be Cameron's. They only see Cameron driving after they open the door and are shocked to see that the driver is black (after Anthony previously bragged about not carjacking black people). Cameron is tired of being pushed around and resists. Anthony tells Peter to shoot Cameron, but Peter does not.
As police officers arrive, Cameron and Anthony both race for the car and jump in. Cameron drives away, with Anthony continuing to point a gun at him. A car chase ensues. Hansen is one of the police officers who has responded and recognizes Cameron's vehicle. Cameron drives into a dead end, puts Anthony's gun into his pocket, and gets out of the car, all the while yelling insults at the officers. Just before he pulls out the gun, Hansen convinces him to stop aggravating the situation and to go home. Hansen vouches for Cameron, fending off the other officers, and promising to give him a "harsh" warning. Later, Cameron tells Anthony that as a black man he is embarrassed for him and drops Anthony off at a bus stop.
Farhad locates Daniel's house and waits in ambush. Just as Daniel's daughter Lara jumps into his arms, attempting to protect him with the "invisible cloak", Daniel's wife Elizabeth (Karina Arroyave) runs out the front door and watches in horror as Farhad shoots Lara. It takes the grief-stricken parents and Farhad a moment to realize that Lara is miraculously unharmed. The box of ammunition that Dorri had selected contained blanks. Farhad later tells his daughter that he believes the little girl was his guardian angel, preventing him from committing a terrible crime. Jean is complaining to someone she knows over the phone that she wakes up angry every day and does not know why. Immediately afterwards, she slips and falls down a flight of stairs, spraining her ankle. Jean phones Rick, telling him of her accident.
Peter, who is hitchhiking, is picked up by Hansen. Peter sees that Hansen has a small statuette of Saint Christopher like his own. He begins to laugh as he realizes that they have so much in common, but Hansen thinks that he is being laughed at. Hansen pulls over and tells Peter to get out if he wants to be "funny". Peter moves to pull the statuette out of his pocket in explanation, but Hansen believes he is pulling out a gun and mistakenly shoots and kills Peter. Hansen dumps the body in the bush beside a road and then torches his own car. Peter is revealed to be Waters' missing brother. Waters and his mother meet at the morgue, where Dorri is revealed to be a coroner and Waters promises to find who is responsible. Mrs. Waters blames her surviving son for his brother's death, claiming he was always too busy to look for Peter.
Anthony returns to the white van owned by the Korean man whom they had run over the night before. Finding the keys still hanging from the door lock, he drives the van away. The Korean man's wife Kim Lee arrives at the previously mentioned hospital looking for her husband, the man who was run over, named Choi Jin Gui. Conscious and coherent, he tells her to go and immediately cash a check that he has in his wallet. The check is most likely payment for the contents of the van. Anthony has driven the white van to a chop shop he frequents, and as they inspect the van, a number of Cambodian immigrants are discovered locked in the back of the van, revealing that Choi was involved in human trafficking. Anthony is offered $500 for each person in the van but refuses out of disgust. Whilst resting in her bed, Jean hugs Maria, saying she is the only true friend she has ever had and apologizes. Anthony drives to Chinatown and sets the Cambodian people free. As Anthony drives away, he passes a car crash, which turns out to involve Shaniqua. Shaniqua and the other driver get out and begin to exchange racial slurs.

Question: Why is Lara hiding?
Answer: She heard a gunshot outside.