Food and feeding is more of a primal instinct, same as when fish in an aquarium look like they are happy to see you, they just know you=food but that is not a hard thing to learn so I would not necessarily say your slugs will be able to do trig, or even learn to jump (slow maybe) through any hoops.

I think snakes are a lot smarter than some think, or want to think compared tho their supreme beingness, but they are not going to play fetch with you either.