They’re Biting

Try not to take it personally if your once cuddly cat or dog is now nipping at you whenever you try to pet them. Odds are that this is just your furry friend’s way of letting you know—albeit, painfully for you—that they aren’t feeling like themselves. In fact, one Spanish study closely analyzed “aggressive” dogs and concluded that, compared to nonaggressive canines, they all had lower levels of the hormone serotonin, which is linked to depression and anxiety.