Dogs, cats, lions, bears, and a number of other mammals self-stimulate with their front paws; randy walruses use their flippers. Horses and donkeys, whose masturbatory habits have been particularly well-studied, engage in "rhythmic bouncing, pressing, or sliding of the erect penis against the abdomen"; male deer do the same. The 19th-century physiologist Karl Friedrich Burdach has even described something like female ejaculation among solitary mares, which "rub themselves against whatever obstacles they find, often spurting a white, viscous mucus." A bull, meanwhile, stimulates itself by alternately protruding its penis from a genital sheath, while some moose can ejaculate simply by rubbing their antlers on bits of vegetation. According to observations made at the University of Buffalo in the 1940s, both male and female porcupines manipulate their genitals with inanimate objects—they're also known to "seize, straddle, and ride sticks about the cage."...