Infinity Eyes
A friend's infinity-sign pupils give away that they're about to talk about dividing by zero.
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Cartoon by Ben Orlin, Math with Bad Drawings. https://cartoons.mathwithbaddrawings.com/2018-03-09-infinity-eyes/ (CC BY-NC 4.0)Transcript
A: "Uh-oh. You've been thinking about infinity again." B: "What makes you say that?"
A: "You've got that creepy look in your eye." B (with ∞-shaped pupils): "Well, since you bring it up, suppose I divide 1 by 0..."