When a train enters a tunnel, it compresses the air in front of it like a piston. Air in a tunnel can't be simply pushed aside--the tunnel walls are in the way.
It sounds fanciful, but Wonka's gum flavored as food is far from impossible if you have the help of a skilled flavorist.
If you chew gum with sugar in it, you need to chew for twenty minutes or more in order to produce enough saliva to wash away a significant amount of the sugar residue. Even then, it’s a good idea to brush your teeth afterward.