pressure
Explanation
The Joke
A person (Sally) smugly states that "a watched pot never boils." Another person corrects her, explaining that a covered pot can reach 350 degrees Celsius, that their vision cannot prevent water from boiling since their eyes are already exerting a pressure of 1000 newtons per square centimeter on the water. Sally then declares "I have so much power" (interpreting the physical facts as meaning she has superpowers), dresses up as a superhero, and attempts to fly — only to be met with a flat "No." from a bystander as she crashes.
The Humor
The joke works through a deliberate misunderstanding of the proverb "a watched pot never boils." The second character tries to debunk the saying with scientific facts about boiling points and pressure, but inadvertently gives Sally the wrong takeaway. Instead of understanding that watching a pot has no effect on boiling, Sally interprets the explanation as meaning her eyes literally exert enormous pressure — and therefore she must have superpowers. The humor escalates from a pedantic science correction to Sally donning a superhero costume and attempting flight, with the deadpan "No." serving as reality reasserting itself. It parodies both the tendency to over-explain simple proverbs with science and the human ability to wildly misinterpret information in self-serving ways.