These 'Scientists' exploit a little known fact about Mentos Mints - if you drop one in a bottle of soda pop (or any other highly carbonated beverage like Coke, Pepsi, Jolt, Seltzer, etc...) it creates a reaction similar to if you had shaken the bottle violently.
The mint, essentially, has a massive surface area upon which to form bubbles - and all this bubble formation at the same time, when you drop the mint in, creates a large amount of gas that has no where to go but up and out of the bottle. The science behind the reaction can be seen here.