professors don't generally say "hello, and welcome to the first day of the semester...this will be a weedout course, just so you know."
in my experience, weedout courses get this name from students looking for an excuse as to why they didn't do well (because we all know it must be the course/professor's fault...
🙄 )
generally, it's organic chem...or sometimes a really intense general bio at some schools. if about halfway through the semester, you start hearing half your class talking about their new majors...it's probably a weed out class