It often feels good - use a small bag of frozen peas wrapped in an old pillow case and just keep refreezing it. It's cheap, doesn't get too icy cold and molds nicely to the area. No longer than 20 mins on if he'll sit still for that long. If you notice it actually keep getting more swollen get it checked, since if he develops a hematoma means a longer recovery, so you want that caught as early as possible and just make sure he stays nice and quiet (which I know is easier said than done). Hope he's feeling better soon!