You can lose your mind trying to understand why cats exhibit certain behaviors. Why do they invite affection, only to greet it with a flash of claws and teeth? Why do they like to hang out in sinks? What is it about cucumbers that terrifies them? And why do cats like to bump heads with their human companions in a cross-species version of a fist bump?

Unlike many cat habits, this one has a relatively clear explanation. Cats have scent glands on their foreheads that release pheromones. Since cats use scents to recognize friendly life forms, a cat rapping its head on yours transfers those pheromones to you, essentially signaling that you’re part of the pack.

This action is actually known as “head bunting,” not headbutting, and is typically reserved for leaders of a cat colony. They may also bunt on your leg or arm.

While you might perceive it as somewhat derogatory—that a cat is marking you as its territory—it’s more affectionate than that. Cats tend to bunt only when they like their target. You can bunt back, or pet them to return the affection.

Keep in mind a bunt is different from a cat resting its head on you, which may be a sign of discomfort and could warrant a visit to the vet.

[h/t PetMD]