Thanks for all the input ladies! I did verify that a baby aspirin every 72 hours is OK for cats. I gave him one Tuesday afternoon and by Wed morning he was his old ornery self again. He isn't limping and there is no sign of infection or swelling in his paw or leg. My suspicion is that he was stung by a bee or other insect - he has had this happen before. Happy to say all is well with my furbaby!