What's missing?

Supposedly helps to improve their thoughts and hence played the game of "What's missing?" with Greg.

Picture 1:

Me: What's missing on this bear?
Greg: No nose
Me: Good job! The bear has no nose!

Picture 2:

Me: What's missing from this bicycle?
Greg: One wheel
Me: Good! You remembered that your bicycle has two wheels and this one has only one wheel, hence, one wheel is missing right?
Greg: Yes!

Picture 3:

Me: What's missing from this squirrel?
Greg: One ear
Me: Ok, one ear is hidden and therefore you don't see it. Besides one ear that you don't see, what is missing on this squirrel?
Greg: One hand
Me: Nope, it has two hands. I give you a clue: Cats and dogs have it, but Gregory don't have it
Greg: I don't know!
Me: Cats and dogs have it at their backside.
Wife: And kangeroos too, they have it at their backside. It's long.
Greg: I know! 大便 ! (Shit)