We’re sure your dog is a very good boy (or very good girl), but you might not know that pooch as well as you think you do.

Myth: Dogs are colorblind, meaning they see the world in black, white, and shades of grey.

Truth: They don’t experience as full of a spectrum of colors as humans do, but they’re certainly not limited to life in monochrome. Humans have three kinds of cone cells in the eyes, which make us trichromatic, and able to see lots of different shades. Dogs, however, are dichromatic, so they have two kinds of cones, which gives them vision similar to that of people with red-green color blindness. For example, the blues they see are similar to the blues we see, while our reds and greens seem to them a sickly yellowish-green.

Myth: Dogs go bonkers when you come home because they’re excited to see you.

Truth: Maybe a little, but it’s mostly just them expelling energy that they built up waiting for you to open the door. Your arrival is the release valve for that energy, and they get it out by jumping on you, running in circles, and barking.

Myth: It’s bad news — and a sign of illness — if a dog’s nose is dry.

Truth: A wet, cold nose is almost as defining a characteristic for a dog as a wagging tail or pettable fur. It’s totally normal and perfectly healthy for a dog to have a dry spell on the sniffer now and then. They’re just like us in this regard — the way our lips or noses get parched during allergy season or because of dry air, the same is true for dogs and their noses.

Myth: One “dog year” equals seven “human years.”

Truth: This misconception-meets-mathematical formula has persisted since the 1400s. It’s just a way humans try to cope with the sad truth that we live much, much longer than dogs on average — about seven times as long. The formula doesn’t work for all dogs across the board, either. For while some dog breeds may live to be 15 (or 95 in human terms), other breeds may top out at 10. (Sorry.)

Myth: A dog’s mouth is sterile.

Truth: With the way their lick and eat almost anything they can get their hands on, inside and out? Or how they bite and lick at themselves? No way.