Cats bite each other's necks for several different reasons. As usual with cats, and all animals, context matters. In adult cats, neck biting is commonly linked to mating behavior. Male cats grasp the female's neck during mating to stabilize her and trigger a hormonal response that allows copulation. This behavior can also appear in neutered cats, where it might be more about instinct than reproduction. Play and learning are another frequent cause, especially in kittens / young cats. Neck biting during playtime mimics hunting and fighting skills. When both cats take turns, keep their bodies loose, and disengage easily, that usually means 'healthy play'. On the other hand, neck biting can appear during conflicts over territory or resources. In this case, a cat biting the neck means it's attempting to control or overpower the other cat. And during this type of behavior, we often see stiff body language, growling, flattened ears, or one cat trying to escape. The hunting instinct plays a role as well. Cats are wired to deliver a killing bite to the neck of a prey. During high-energy play (or tension), this instinct can spill over onto another cat. Less commonly, sudden or excessive neck biting can be linked to medical or neurological issues or hormonal imbalances. Dental issues are also a possible cause, though they're not a common primary cause on their own. But certainly, pain from a gum disease or an oral infection can lower a cat's tolerance and impulse control. A cat that's uncomfortable may bite more quickly or react aggressively during play or social interactions. In multi-cat households, this can show up as sudden roughness toward a familiar cat. As for kittens, gentle neck biting can be related to nursing behavior, as they instinctively associate the neck and scruff with safety and maternal handling. Eventually, neck biting might become a concern if it causes wounds, fur loss, fear or ongoing stress, or when one cat is consistently targeted. As cat parents, we can help avoid this at home by increasing environmental enrichment and separating high-conflict cats during peak tension. Finally, it's best to ensure the cat(s) is spayed or neutered and contact a vet if the biting issue escalates or appears suddenly.