How do mints make your mouth feel cold?

And is it really colder after you’ve eaten one? That’s gotta violate some laws of thermodynamics, right?

No thermodynamic laws get violated. Your mouth doesn’t actually get any colder, but it feels colder because of a sensory trick. Just as the capsaicin in hot peppers creates a burning sensation by stimulating your heat-sensing nerve endings, the menthol in mint products creates a cooling sensation by stimulating your cold-sensing nerve endings.

This is also why the kids I used to work with would come up to me with a big burn that some idiot adult had put toothpaste on. Toothpaste on a burn! Pff… (Not saying that you would do that at all, just an illustration of the ignorance we are all so bravely fighting!)