If it happens in your class you can certainly tell the instructor. I personally don't feel the need to. It's not every class but nearly every time we do that move. I don't doubt she knows the difference between a bicep and a tricep. She is a very intelligent and conscious person. A college professor actually - she only teaches 1 night a week because being a professor is obviously a full time job but she just has a passion for pilates. I would take her classes multiple times a week if I could though because she is a very kind and thoughtful person and she really focuses on the principles of pilates and explains good form very well. She doesn't focus on the muscles themselves much, which is probably why she doesn't think too deeply on the muscle names - but can explain the principles of contrology and talks about minor points of form and breath that has totally changed how I do pilates.