Trim your pets' nails. I can't tell you how many times I've had to wrestle an ingrown nail out of an animals flesh. And that stuff can get in there deep. And most of the time, the animal doesn't give you any signs that it's in pain and the owners don't even notice it's happening

Edit: As many have pointed out, there may be some instances of NOT needed to cut your pets nails. Your pet may grind them down themselves from scratching posts or walking on concrete surfaces or digging up your yard. Keep an eye on nail lengths and use your best judgement. If you think they are getting long, trim them yourself or take them to a groomer or veterinarian