The Nobel Prize winning chemist Melvin Calvin (1911-1997) was not known as a man of great humor. This only encouraged one of his assistants to play a great prank on him while Calvin was preparing a paper for a 1955 issue of the Journal of the American Chemical Society. Joshua Howgego, a graduate student in chemistry, describes it:
I wasn’t lucky enough to ever meet Calvin (he died in 1997), but according to Kilcoyne he was a serious man with little patience for jokes or pleasantries. This contrasted starkly with his graduate student, A. T. Wilson, who was, it would seem, a bit of a practical joker. Wilson reputedly made a wager with his departmental secretary that he could sneak in a picture of a man fishing into one of the diagrams in a forthcoming paper without his supervisor noticing. He won his bet and the fishing man is still in the diagram today. Calvin never found out.
Do you see the fisherman? Here he is: