Mental blocks

The Zippy strip of 8/24: The answers are: George Costanza and Leonardo da Vinci Extracting content from Wikipedia: a mental block is a temporary inability to recall a name or other information (the sense here, and utterly commonplace) or: an inability to continue a train of thought (more worrisome) or: the suppression of painful or unwanted thoughts (even more grave) Zippy sees the mental blocks as literal but ghostly (alphabet) blocks that he can play with, juggling them in the air. But then Zippy is only visiting our world.