It is very important for you to keep a controled balanced weight of your piggy(s). The better way to notice if something is wrong with your piggy is by checking the piggy's weight. In the wild they are the prey of predators, that means that by nature they won't show you they are hurt, sick, injured or anything, but they will stop eating or you will noticed a change in their behavior. So it is very important for you to keep an eye on your piggy's behavior and weight. What I do is I set a day of the week and every one on the same day I weight my 4 piggies to see how they are doing. If you notice that your piggies has lost 1-2 oz it is ok but check on them, if you noticed 4 oz lost in just a week keep an extra eye on the piggy because there might be a problem. If you see that your piggie has lost more than 4 oz I HIGHLY recommend you to go to a vet ASAP. Sometimes it is nothing but sometimes it is a sign of illness or stress.