Chances are your dog is a little on the older side.
if it is black it may be that your dog is getting old or it is dirty.
if it is a BRUISE, your dog will be very very lethargic and wont want to get up and play or swim or fetch. Chances are it wont do or even refuse to do anything. If this is the case take your dog to the vet asap. Because this means it is bleeding on the inside and can cause damage.
