If you attack the correct "Eye" of a Magic Pot, you can get bonus items. If you attack the wrong "Eye," you will be hit by a physical Area of Effect attack.

I've yet to be able to attack it correctly more than twice, but the value/rarity of the items given increase for every "Eye" hit correctly in sequence. Too bad that the sequence is random...

Tonberries appear more frequently in the back of the caves. You can also go into the hidden vault rooms for a much higher frequency of encountering Tonberries. The Cavern of the Stolen Fayth is also the only place where you find Tonberries in FFX.