Dog

A professor must have a theory as a dog must have fleas.

~ H.L. Mencken

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I am pretty sure that I was a dog in a former iteration.  I know how to do things like sit, stay, and shake.  I think I was probably not a retriever, though, because if throw something and tell me to run and get it, I'm likely not to do it.  And also, it is likely that I will think you are a moron.  

(pause)

Or maybe I was a cat.