Mario Punching Yoshi - Two things to debunk the “Mario hits Yoshi on the head to make him extend his tongue in Super Mario World” theory:

Another thing to consider is, wouldn't it be faster to train yoshi to eat whatever is in front of him by physical stimulus (like a hit or pat on the head) rather than pointing forward and telling him to eat whatever is in front of it?

I mean it's easier to coordinate by stimuli than verbal communication.