Under "Hobbies" or "Other" as "exhaustive study of English fantasy literature?" If the application is to vet school, however, try including this: Although, in all seriousness, if it's AMCAS the OP is talking about, then yes, there is a place to enter in hobbies.
Only include this if your resume is really, *really* sparse. It has no place on a CV, and I'd hesitate to include it in the AMCAS profile.
how about hobbies like tennis? I played varsity tennis in high school and in college I only play recreational tennis through my college tennis club. But I didn't compete or play IM, just for fun.
Never, ever do this. It's extremely unprofessional to list hobbies and interests on any resume. If an interviewer wants to get a feel for your personality, they might ask you what your interests are outside of work, but to present it plainly on your resume is generally a bad practice. It should be limited to high school students looking for a part-time job or college students with little to no experience.