Not necessaraily a brain tumor either. May be something is causing him pain, and touching him made it hurt. Even if you didn't touch the exact spot making him move could have jarred something sore. Cats are known to get abcesses fairly easily with tiny cuts that can be hard to find, and he and Forest have been arguing. Maybe he got clawed somewhere, just a little, and it is now sore? A vet is still a good idea, it could be something serious and if not they can reassure you that things are all right.
Dr. Seuss~DLH (brother's cat)~June 2007-
Misty~DSH (my cat & Mooby's mom)-?-
MooBoots(Mooby) ~ DMH(Mom's cat)~July 21, 2008-
Sunshine~ Golden retriever X white german sheperd (Dad's dog)~October 24, 2008-