Mission: Impossible

Several years after the events of the series, Jim Phelps and his team, the Impossible Missions Force, attempt to retrieve the IMF non-official cover list from the American embassy in Prague. Their mission fails: Phelps is shot, his wife Claire seemingly dies in a car bombing, and the rest of the team except agent Ethan Hunt are eliminated by unknown assassins. Meeting with IMF director Eugene Kittridge, Hunt reveals his awareness of a second IMF team sent to keep an eye on them, and learns the job was a setup to lure out a mole within IMF. The mole is believed to be in contact with an arms dealer known as "Max" as part of "Job 314." As Hunt is the only member left, Kittridge suspects him of being the mole, and Hunt flees.
Returning to the Prague safe house, Hunt realizes "Job 314" refers to Bible verse Job 3:14, with "Job" as the mole's code name. Claire arrives at the safe house, explaining she escaped the bomb after Phelps aborted the mission. Hunt arranges a meeting with Max, where he warns her that the list she possesses has a tracking device. He promises to deliver the real list in return for $10 million and Job's identity. Hunt, Max, and her agents escape just as a CIA team arrives.
Hunt recruits two disavowed IMF agents: computer expert Luther Stickell (Ving Rhames) and pilot Franz Krieger (Jean Reno). They infiltrate CIA headquarters in Langley, Virginia, steal the real list, and flee to London. Kittridge, detecting the theft, has Hunt's mother and uncle falsely arrested for drug trafficking. He provides media coverage of the arrest, forcing Hunt to contact him from Liverpool Street Station. Hunt allows the CIA to trace him to London before hanging up, but is surprised to find Phelps nearby. Phelps recounts surviving the shooting, naming Kittridge as the mole. Hunt realizes Phelps is the mole, having discovered that Phelps stole a Bible from a Chicago hotel. He also suspects Krieger as the one who killed the other IMF members on the Prague job, but is unsure whether Claire was involved. Hunt arranges with Max to exchange the list aboard the TGV train to Paris the next day.
On the train, Hunt remotely directs Max to the list. Max verifies it and gives Hunt the code to a briefcase containing the payment along with Job in the baggage car. Ethan calls Claire and tells her to meet him there. Meanwhile, Stickell uses a jamming device to prevent Max from uploading the data to her servers. When Claire reaches the baggage car, she finds Phelps, and tells him Ethan will arrive shortly. She questions the idea of killing Ethan, since they'll need a fall guy for the money. To Claire's surprise, Phelps reveals himself to be Ethan in disguise, exposing her as a co-conspirator. Moments later, the real Phelps arrives and takes the money at gunpoint. Hunt dons a pair of video glasses that reveals Phelps' existence to Kittridge, proving that Phelps is the mole.
With his cover blown, Phelps tries to kill Ethan. Claire intervenes and Phelps kills her. He climbs to the roof of the train, where Krieger is waiting with a helicopter and a tether. Hunt stops Phelps from escaping and connects the tether to the train itself, forcing Krieger to pilot the helicopter into the Channel Tunnel after the train. Hunt places an explosive chewing gum on the helicopter windshield, killing Krieger and Phelps. Kittridge arrests Max and recovers the list, then reinstates Hunt and Stickell as IMF agents, but Hunt resigns. As he flies home, a flight attendant approaches him and asks, through a coded phrase, if he is ready to take on a new mission, just as she asked Phelps at the beginning.

Question: What does Hunt place on the helicopter windshield?
Answer: explosive chewing gum