Shuttle

The film begins at the airport, where two friends, Mel (Peyton List) and Jules (Cameron Goodman) are getting off their flight. Mel has motion sickness, and Jules tells her to take a minute to calm down. Seth (James Snyder) and Matt (Dave Power) arrive and introduce themselves to them. Jules takes Mel into the bathroom, where Mel tells her that she has broken up with her fiance.While they are waiting for their baggage, Mel communicates with a deaf girl, showing off her sign language skills, and Jules waits for the bags. Jules gets her bag, but Mel's isn't there, and the people at the airport tell her that she will need to come back the next day and collect it. They go outside and wait for a shuttle bus and one pulls up. The Driver of another bus (Tony Curran) tells Mel to ask the bus driver how much he will charge and he tells them $60. The Driver says he will do it for $30. They arrive on the bus and are greeted by the creepy Andy (Cullen Douglas). Seth and Matt arrive, and The Driver tries to get them to go away, but Jules tells him that the guys are with her.They board the bus, and Seth sits next to Jules, with Matt sitting next to Mel. The driver takes a strange route, and Mel decides to show Matt her signing skills. After this, they are run off the road by a strange car, and the Driver gets out to survey the damage. He tells them that they have a flat tyre. Jules opts to call a taxi, but there is no service where they are. Matt offers to help change the tyre. While his hand is on top of the tyre, The Driver looks for some nuts for the wheel. Mel turns her back for a second, and the bus falls on Matt's hand. When they get it up, his fingers have been cut off. Seth gives Matt his shirt to cover his fingers, and they drive off to the hospital.Later, it appears that The Driver is lost, and he pulls out a map. Seth starts to get mad at him, until he pulls out a gun and orders them all to sit down at the back. He tells them he wants money. Andy offers his wallet, but he refuses to take it. He takes everyone's phones from them instead. Mel and Seth argue about doing something, and Mel tells them that they need to stop what is going on. Jules finds a flare under the seat, and Mel comes up with a plan to get the window open. Andy sees her and causes a commotion, with Seth getting involved too. Andy pulls the lid off, and Mel throws the flare into the boot. The Driver sees this, stops the bus and removes the flare. Jules runs for the front and finds the door locked and the key missing. She beeps the horn instead.The Driver re-enters and points a gun at both Seth and Andy. He pretends to shoot Andy but instead pulls out a switchblade and slashes Seth's face. He drives them to an ATM booth, and Jules goes in to get some money out. While she is inside, she knocks some paper into a bin and sets it on fire. The Driver sees this, and rushes towards her, but she slams the door. Mel escapes, but The Driver shouts at her that he will let Jules suffocate if she doesn't come back. She has no choice but to surrender.He then takes them to a supermarket, where he tells Mel to go inside with the money and buy some supplies and a large bottle of water, and nothing else. He tells her if she tries to alert anyone he will kill everyone. On the bus, he chains Seth and Andy together and makes them take people's valuables and passports from their bags, and tells Jules and Matt to strap themselves in so they can't escape. Seth tells Andy if he gets loose, The Driver can only get one of them. Mel sees a security camera and signs into it that she needs some help, before giving the cashier a note telling her to check the security tapes when she leaves. Seth gets free and makes a run for it, only to be run over by the bus right in front of Mel. The Driver then reverses over him just to make sure he is dea, before dragging Mel back on to the bus.He then scolds Mel for buying ice when she didn't need to, but she tells him it's for Matt's fingers. Back in the store, the cashier checks the tapes only to find out they were never switched on. Later, Mel shows Matt a knife she hid in the ice, which she uses to cut her belt off. She then cuts Matt's off, Matt uses the ice bag to smash the window, and they all shout for help, but no one can hear them. The Driver walks towards them and pulls out the gun, so Mel cuts his wrist with the knife. Matt then hits him over the head with the bag, as Mel grabs the gun and threatens to shoot The Driver. She makes him hand over the keys to the belts, and Jules is able to get herself free, and gives them to Andy. Mel tries the radio, only to find that it doesn't work. She then makes him take his knife out, but he throws it into one of the seats.She takes the wheel of the bus and drives away, leaving Matt with the gun and Andy with the knife. Andy then nonchalantly stabs Matt in the throat, which no one notices at first. He grabs the gun and puts it to Mel's head, telling her to get away from the pedals. Andy then reveals himself to be in league with The Driver, and the pair torment the girls for a while, forcing them to put belts on. Andy assaults the girls until The Driver gets him to stop. He drives to a bridge and they throw the bodies off.Later, Mel manages to get a tyre iron from under the seat, and keeps it by her side. Andy wraps tape around Jules' mouth and then does the same to Mel. He then cuts a piece each from their hair. Mel hits him several times with the tyre iron and The Driver is forced to stop. She pulls herself free, and The Driver attempts to get the gun, only for her to hit him on the hand, and knock it towards Jules. Mel seizes control and drives away, but he rushes towards her. She slams the brakes on and he falls, then accelerates again so he falls backwards. She reaches for a knife, but it is too far, so she swerves to get it closer to her, and The Driver reaches for the wheel. She stabs him in the knee, and Andy comes over to attack her. She grabs a fire extinguisher and hits him with it, but crashes into a wall.Jules escapes the crash and flags down a passing car. A man gets out, but before he can help her, he is run over by the bus. Jules is then forced back on to the bus where they drive to a warehouse. The Driver makes Jules dye Mel's hair blonde, so she will look better, and then makes them strip down to their underwear for an inspection. The man who inspects them is revealed to be the man that ran them off the road, who then gets in his car and leaves. The Driver inspects their bags and finds that Jules has taken pills for a yeast infection, so he takes her on to the bus and gasses her.He finds Mel, who threatens to cut herself with a shard of glass, and she stabs him in the arm with it. He attempts to disarm her, but she stabs it into his thigh before hitting him in the face with the light fittings. She finds the gun and shoots him, before attempting to escape in the bus. The Driver arrives and attacks her again, and they grapple before he forces her into a crate with the supplies she bought earlier.She examines a photo and sees some sex slaves, before the crate is loaded onto a ship. It becomes clear to her that she is to be sold as a sex slave, and the supplies are for her trip to Asia. The final shot is of Mel's bag turning up at the airport, as another day begins.

Question: Why does Mel go to the bathroom?
Answer: Motion sickness.