Snakes on a Plane

After witnessing gangster Eddie Kim brutally beat U.S. Prosecutor Daniel Hayes to death in Hawaii, Sean Jones is escorted by FBI agents Neville Flynn and John Sanders on a Boeing 747-400 to testify in a trial in Los Angeles. Despite increased security for the flight, Kim arranges for a time-release crate full of venomous snakes to be placed in the cargo hold in an attempt to bring down the plane before it reaches Los Angeles International Airport (LAX). To ensure the snakes attack the passengers without being provoked, he has one of his henchmen disguised as an airport ground employee spray the passengers' leis with a special pheromone which makes the snakes highly aggressive. The crate opens midway through the flight and the snakes make their way through the cabin. A couple having sex in the bathroom, and a man using the bathroom are the first killed. The plane's captain, Sam McKeon, investigates and fixes an electrical short, but is killed by the viper that caused it. Co-pilot Rick, unaware of the snake, believes Sam has suffered a heart attack and continues toward LAX.
Some of the snakes attack Rick, and while fending them off he accidentally releases the oxygen masks throughout the plane, causing several snakes to drop into the cabin with them. Numerous passengers, including Agent Sanders, are killed when the snakes invade the cabin. The surviving passengers, who have made their way to the front of the plane, put up blockades of luggage in a desperate attempt to stop the snakes. Rick is attacked and the plane starts to dip downwards, causing a food trolley to crash through the luggage blockade. The passengers flee to the upstairs first class cabin before blocking the stairwell with an inflatable liferaft. Agent Flynn and Flight Attendant Claire regain control of the plane. Rick retakes the controls and has Flynn go into the cargo hold to restore the air conditioning/ventilation system. Agent Flynn contacts FBI Special Agent Hank Harris on the ground, who gets in touch with ophiologist Dr. Steven Price (Louiso), Customs' main source for animal smuggling cases. Based on pictures of the reptiles emailed to him via a passenger's mobile phone, Price believes a Los Angeles snake dealer known for illegally importing exotic and highly dangerous snakes to be responsible. After a shootout, the dealer is bitten by one of his snakes and Harris withholds the antivenom if he does not give them details. The dealer finally reveals that Kim hired him to obtain the snakes and adds how the latter managed to smuggle them on board the plane. Price injects antivenom to the injured dealer and he commandeers the dealer's supply of antivenom for the plane's victims based on the list given to him, while Harris gives orders to have Eddie Kim arrested on multiple counts of murder and attempted murder.
Harris contacts Flynn, telling him that anti-venom will be ready for the passengers when they land. However, Flynn discovers that the cockpit is filled with snakes and Rick is dead. After a brief discussion, Troy, Three Gs' bodyguard, agrees to land the plane based on prior experience. After everyone gets prepared, Flynn shoots out two windows with his pistol, causing the plane to depressurize. The snakes are blown out of the cockpit and the lower floor of the plane. Flynn and Troy take the controls of the plane and Troy reveals that his flight experience was from a video game flight simulator. Despite his lack of real-world experience, after Troy makes an emergency landing, the plane makes it to the terminal. The passengers leave the plane and anti-venom is given to those who need it. Just as Flynn and Sean are about to disembark the plane, a final snake jumps out and bites Sean in the chest. Flynn draws his gun and shoots the snake, and paramedics rush to Sean, who is unharmed due to a bulletproof vest. As a token of gratitude, Sean later takes Flynn to Bali and teaches him how to surf.

Question: What dropped into the cabin with the oxygen masks?
Answer: Snakes