The Biodiversity Heritage Library has digitized Charles Darwin’s annotated library. This annotation in The Natural history of Mammals from Paraguay compares his son to some animal (I think a monkey):
Text: “ if he is caught, he begins immediately, for fear of punishment to scream. If he can devour his prey, unseen, he is afterwards so innocent and unafraid, as if nothing happened.”
Annotation: “Lenny did this. Emma often perceived he had been on dining room on the table & found it so.”
This is the kind of thing I love about libraries.