In the humorous exchange in the Avengers I， Bruce said:
“I don’t think we should be focusing on Loki,” Bruce said. “That guy’s
brain is a bag full of cats. You can smell the crazy on him.”Thor took a step toward Bruce. “Have a care how you speak,” he warned.
“Loki is beyond reason, but he is of Asgard . . . and he is my
brother.”“He killed eighty people in two days,” Natasha pointed out.
Acknowledging this, Thor backed down a little. “He’s adopted.”
I could not locate the exact meaning/implication of "cats" here. So far I have three guesses:
1) There is a phrase "let the cats out of the bag", meaning secrets leaked; so does this mean "Loki's head is full of (dark) secrets?
2) According to Collings dictionary: "a bag of cats" is an Irish informal way of speaking someone "bad-tempered"; so does this mean "Loki is a bad-tempered person? (which I personally don't think it fits the context and the usage of Irish English does not make sense to me in an American movie.)
3) In my culture, cat has some connotation of "smart\clever", which leads to "sly"; so does this sentence mean "Loki's brain is very smart and he is sly?"
Anyone could help me with the "cats" here please? Thanks a lot.
Best Answer
"A bag full of cats" is an Irish expression for a bad-tempered person and that does seem the closest definition to what is intended here. However, that isn't widely known and I'm not sure that is what influenced your quote from Avengers.
Not all metaphors and expressions are out of a book - some are made up on the spot! I think the writer just thought that cats can act crazy, a lot of cats in a bag would act super crazy, so let's say this crazy guy's brain is a bag of cats!