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  • If you have a dog you've probably heard that chocolate will make your pet sick,

  • and that also applies to other pets like cats, rats, and mice.

  • but that just doesn't seem fair.

  • Why do we get to go to town on a giant bar of dark chocolate

  • but Fido shouldn't even have one bite?

  • It all has to do with a molecule called theobromine

  • which is made up of carbon, hydrogen, nitrogen and oxygen atoms.

  • And along with its partner caffeine, is one of the many reasons

  • humans have loved chocolate for thousands of years.

  • Both molecules are dangerous for dogs but chocolate contains

  • a lot more theobromine than it does caffeine

  • so it's the molecule to watch out for. Like caffeine,

  • theobromine is a type of alkaloid, which is a huge class of molecules

  • that generally contain rings with at least one nitrogen atom in them

  • and alkaloids often have physiological effects on humans and other animals.

  • Also like caffeine, theobromine makes our heart pump faster,

  • our blood vessels dilate, and some of our muscles

  • get more energy, which sounds great!

  • But, too much of it can make our hearts pump too quickly

  • and our muscles contract uncontrollably,

  • eventually leading to nausea, convulsions, heart attack, and even death.

  • Luckily for our taste buds, we humans process theobromine pretty quickly,

  • so that's not something you have to worry about.

  • It rarely sticks around long enough to cause any harm.

  • But, our pets aren't so lucky. They process theobromine a lot more slowly,

  • so it can easily build up and cause those dangerous effects.

  • It's hard to know exactly why we evolved to be better at digesting theobromine,

  • but it might be because alkaloids mostly come from plants,

  • and our ancestors ate a lot more plants than early cats or dogs did.

  • Whatever the reason, the same amount of theobromine

  • stays in pets' bodies much longer,

  • giving it more time to pile up and cause harm.

  • On top of that, most pets are a lot lighter than humans,

  • so it really doesn't take much chocolate to make them sick.

  • Cats don't often get poisoned from chocolate

  • because they can't taste sweet things,

  • so they're generally not too interested in it,

  • But, dogs sure are.

  • Your average adult human would need to eat about 8 kilograms of dark chocolate

  • to get a lethal dose of theobromine.

  • But, a medium-sized dog would only need to eat about one kilogram, and

  • a house cat would only need a tenth of a kilogram.

  • Sweeter chocolates have less theobromine, so the lethal dose is higher;

  • about 5 kilograms of milk chocolate for dogs and about a third of a kilogram for cats,

  • but they'd be sick long before eating that much.

  • Meanwhile, you and I will have to eat about half of our body weight in milk chocolate for a lethal dose,

  • which might sound wonderful, but I don't want to see any of you writing "challenge accepted" in the comments,

  • because you'd be very sick way before finishing that much chocolate.

  • Among other things, I'm trying very hard not to picture what that would do to your digestive system

  • But the next time you decide to indulge in a chocolate bar,

  • or three,

  • just keep it to yourself, no matter how long your dog gives you those adorable puppy eyes.

  • Thanks for asking, and a special thanks to our patrons on Patreon who keep these answers coming.

  • If you'd like to submit questions to be answered,

  • you can go to patreon.com/scishow,

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If you have a dog you've probably heard that chocolate will make your pet sick,

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