Jake knows what pigs are, as in real animal pigs. (of the oink, oink variety) He also knows that his feet/toes can be called piggies. Apparently, what he doesn't know is the distinction between them sometimes.
Jake was looking for a particular book the other day; the book was on his bookshelf and on top of his bookshelf is a piggy bank. This was what happened when he got the two "piggies" confused:
Jake: *wandering around the playroom, looking for his book*
Me: Jake, your book is on your bookshelf.
Jake: *blank stare*
Me: On your bookshelf, right under your piggy!
Jake: *lifts up one foot & looks under his 'piggy' for the missing book*