system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: In the expression, "Teaching grandmother to suck eggs", what is the meaning of the concept of sucking eggs?
gpt
Sucking an egg is when you make two small holes in the shell, one in each end.  You then suck the innards out, leaving a pristine shell that can be decorated.

edit: to elaborate, crafting painted eggs is a stereotypical old timey female activity.  So to teach your grandmother how to do that craft would be teaching an expert something obvious, kind of like educating the Pope on Catholicism.  Make sense?