I went looking for the exact marmot quote from the movie and ended up on a trivia page that had this delightful tidbit:

A marmot was originally planned to be used in the bathtub scene but a ferret was swapped in once the Coen Brothers realized that a marmot would be too large for filming purposes.

I thought they were just playing ignorant at not knowing what a ferret looks like but the fact that they pivoted on the animal during production and didn’t change the script is hilarious.