[Abby panting]   You've seen dogs do it and you know it's called panting - even though dogs don't wear pants. But have you ever wondered why they do it? You and I don't seem to do it. Cats and other mammals do it very occasionally. But dogs and their relatives are best known for it, and for good reason.    Panting is one way, the main way really, that dogs release heat in order to lower their body temperature. Humans do this mostly by sweating, of course. When you get hot and start to sweat, your body heat excites the water molecules on the skin. Some of them get so hot that they evaporate away, leaving the cooler molecules behind. Those molecules escaping into the air take the heat energy with them, leaving you cooler. So evaporation removes heat from a liquid, which is how sweating cools us down.   Now you may have heard that dogs can't sweat, but that is not true. Dogs do have sweat glands, but only their paw pads. And that is not enough surface area to keep the dog's whole body cool, especially when they spend so much time standing and walking on their precious paws. So to make up the difference, dogs release that heat through the evaporation of their saliva, in addition to their sweat.    With all that hard and fast breathing, more water than usual evaporates from their mouths and throats, and even their lungs. This removes a lot of heat really quickly, even from the inside of their bodies. But it also means that they need a lot of water when they're hot because they lose a ton of it through that evaporation.    And panting is more than just heavy breathing. Dogs also let their tongues hang out of their mouths when they pant, not because they're tired or lazy, but because it makes their saliva evaporate even faster. If you've ever gotten a loving lick from a pup, you've no doubt noticed that their tongues are long and flat, creating a lot of surface area for evaporation. They're also packed with blood vessels, so the blood can be cooled quickly before reentering the core of the body.    So even though it's slobbery and messy, panting is a really remarkably complex and efficient system. So why don't all of our furry friends use the same system then? Why don't we pant? Well we do! All mammals, even humans, pant under certain conditions such as extreme heat, over-exertion, or allergic reactions. But most of us have lots of other ways of keeping cool. Cats and kangaroos ,for example, lick themselves and let their saliva evaporate that way. Other animals, like pigs and hippos and elephants, coat their bodies with mud and are cooled as the water evaporates from that.    So the next time your dog looks like this, give her some water, maybe a hug, and then both of you take a moment to be thankful for the process of evaporation.   Thanks for watching this SciShow Quick Question. If you have a quick question for us you can ask us on tumblr, or facebook, or twitter, or in the comments below. People who subscribe to SciShow on subbable.com get these questions answered a little bit earlier than the rest of you. So you might want to check that out at subbable.com/SciShow. Thanks for watching. Don't forget to go to youtube.com/SciShow and subscribe.