They’ve been by your side for years, and you think you know everything about what makes Fido and Fluffy tick. Well, maybe not. The minds of dogs and cats are very different from those of humans, and not every behavior means quite what we think it does. Here are some of the most commonly misinterpreted:

Dogs licking babies: Videos of this are all over YouTube, and people often think it’s adorable and amusing. But that licking can mean the dog is stressed out, according to trainer Susan Marett of Purely Positive Dog Training in Mount Pleasant, because the baby often has a grip on the dog’s fur. “All other body language points to the fact that they’re uncomfortable,” she added. The licking “is an effort on the dog’s part to get away.”

Dogs sniffing other dogs’ behinds: This is a standard canine greeting, according to trainer J.R. Johnson of Charleston Dog Wizard, but often owners are weirded out by it or make their dogs do it by sitting down — when they’re wired to do it standing up. “Sniffing butts is the dog hello,” Johnson said. “We want them to sit in this perfect pose, facing the other dog, when that is actually more stressful for the dog. That’s how we shake hands, and we want our dogs to do it in the same way.”

Dilation of the eyes in cats: While cats are perhaps a bit more mercurial than their canine brethren, this is a pretty clear sign they’re agitated, according to Mary Beth Dew of Adopt Charleston Cats. “A lot of people will look at dilation of the eyes and think, ‘Oh, you want to play,’” she added. Look for flattened ears and a fluffed tail as further evidence of unrest.

Dogs appearing protective: A dog barking or growling at a visitor is often seen as a sign of the animal being protective. In truth, it can mean the dog perceives its human as weak, and feels the need to assert its own dominance, according to Jeff Schettler of GA K9 South Carolina. A true alert posture is ears up with head and tail high, the dog showing confidence — but not acting out.

Tail wagging in cats and dogs: A wagging tail is a good thing, right? Well, not always. Especially not in a cat, where a wagging tail can mean a sign of agitation. A happy cat is often one with its tail curled up over its back, Dew said. In a dog, a raised, wagging tail is typically a good sign — but not if the tail is held low, flicked back and forth, and combined with other traits like pinned-pack ears or a rigid posture.