As an undergrad, I signed up for an English Department elective called “Satire” because the professor was a relatively well known author and I thought it would be fun. He stressed during the first class that it was intended for English majors only, and if anyone wasn’t they should drop the class.
I kept quiet, got an A, and had a paper I wrote published in the department’s magazine. The professor approached me after the last class to let me know he’d investigated me and now knew I was a biochemistry major. He laughed about it.
The next term I took a Physics & Science Fiction elective that was an upper level physics course. I thought it would be fun. It was the most difficult course I ever took, more work than Organic Chemistry.