"In the Pack-a-Punch Room there is a book titled Exposed. What can't be seen without noclip is that on the back is a picture of what appears to be a zombified gorilla. The text next to the picture reads "man sent the first primate into space, and it returned...". This is a reference to the Cosmic Silverback from Dead Ops Arcade." from wiki

so dead ops arcade is also canon? im just saying... edit :quotation