suppermariobroth:

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

1. As you can see in the slowed-down animation, Yoshi contorts his face before Mario’s hand overlaps his head, showing it is not an impact that triggers his action. 

2. The official art suggests Mario is simply pointing forward to show Yoshi what to lick, and the graphics lack the detail to show that.