The poem describes a babysitter named Mrs. McTwitter who believes her job is to literally sit on top of the baby rather than watch over it, showing her to be a strange and potentially dangerous babysitter.

1. The Baby–Sitter
Shel Silverstein
Mrs. McTwitter was the baby-sitter
I think she's a little bit crazy.
She thinks a baby-sitter's supposed
To sit upon the baby.