Imagine accidentally biting your tongue with razor sharp teeth, or going to scratch an itch and having your claws out by accident. How about being overly-receptive to foul smells due to an extremely sensitive olfactory system? Good luck finding a set of glasses to fit over non-human ears as well. Also, if your lineage involved predatory animals, the increased refresh rate of your eyes would mean you would need a special TV or computer monitor to see everything correctly. Lots of complications would become apparent, as you can imagine.