Why do dogs hump things?

According to the ASPCA, humping objects, other animals and people is normal behavior for most dogs and is done by both males and females. Dogs may mount objects or other living things if they are experiencing stress, sexual tension, feeling playful or suffer from a compulsive disorder.

Male dogs commonly mount other dogs or animals if they are in heat, which occurs more frequently if a male dog is not able to access a female dog that is in heat. Dogs also behave in a sexual manner towards people and animals to demonstrate their social status or exhibit control. This type of behavior is commonly practiced by male and female dogs, even after they are neutered or spayed.