I believe it’s a reference to a Discworld personage The Librarian is known for his violent reaction whenever he hears anyone refer to him as a "monkey" (orang-

I believe it’s a reference to a Discworld personage The Librarian is known for his violent reaction whenever he hears anyone refer to him as a "monkey" (orang-utans are apes). He speaks an elaborate language whose vocabulary consists of the single word Ook (and its antonym "eek" - where "ook" means yes, "eek" tends to mean no) https://discworld.fandom.com/wiki/The_Librarian https://discworld.fandom.com/wiki/The_Librarian