Hank: Have you ever been snacking on some sashimi and paused to wonder: why do we eat raw fish but not raw chicken? Really, eating any kind of raw meat comes with some health risk to humans, depending on how it was slaughtered, stored, and prepared. But some are more iffy than others, because different animals have different microbes and parasites inside them, some of which are really nasty to humans.

Fish is on the safer end of the spectrum. It doesn’t usually carry bacteria that are harmful to humans, but we do have to watch out for parasitic worm larvae like, tapeworms, or flukes. If you eat infected raw fish, the larvae will mature into worms that can latch onto organs and cause some serious damage.

Sometimes fish is frozen for storage, and if it’s cold enough, any parasites or bacteria hanging around will die. But cooking fish is the best way to make sure everything infectious stuff is gone. But if your sushi comes from a clean, reputable kitchen, it’s probably safe to eat.

Now, what about other meats, like beef, chicken, and pork? The bacteria that live in these animals, like strains of Salmonella and E. coli, tend to be more dangerous to humans than any that live in fish. Many harmful microbes live in cattle guts, not the muscle where we get cuts of steak.

But beef can be contaminated if a butcher punctures the digestive tract. So steaks might have bacteria on the surface. Usually a good, hot sear is enough to kill off anything infectious, and leaving the inside red is fine, because it's sterile in there.

Ground beef is more treacherous, because any germs living on the surface of the meat get mixed inside. Plus, it tends to contain meat from multiple animals, so one contaminated cow means bad news for an entire batch of ground beef. That’s why you should probably not order totally rare hamburgers -- they should be cooked all the way through.

The meats firmly on the dangerous-when-raw list are chicken and pork, which might be carrying even more harmful microbes than beef. Infectious, diarrhea-causing Campylobacter strains can live in chicken guts. And the crowded, dirty conditions at many chicken farms mean that lots of raw chicken may be contaminated.

Pigs, on the other hand, have historically harbored the parasitic worm Trichinella spiralis, although modern farming practices mostly prevent it from spreading. The larvae form cysts inside the muscle tissue of pigs, so if you eat infected, under-cooked pork, some worms will make a home in your guts. So sushi and rare steaks can be delicious when they’re prepared safely, but you should always pass on the pork tartare.

Thanks for asking, and thank you especially to all of our patrons on Patreon who keep these answers coming. If you’d like to submit questions to be answered, or get videos a few days earlier, you can go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow and subscribe!