Notes:

My edit based on a scene from SpongeBob SquarePants episode "I'm with Stupid" in which SpongeBob said "It's normal size and fully functional" (talking about his brain). The main image is from "Graveyard Shift".
The text sources are from the following title cards:
"NORMAL": "Not Normal"
"SiZE": "Opposite Day" and "Pizza Delivery"
"And": "Mermaid Man and Barnacle Boy V"
"FULLY": "F.U.N." and "The Bully"
"FUNcTioNAL": "F.U.N." and "Mermaid Man and Barnacle Boy VI: The Motion Picture"