What’s the weirdest thing you learned this week? Well, whatever it is, we promise you’ll have an even weirder answer if you listen to PopSci’s hit podcast. The Weirdest Thing I Learned This Week hits Spotify, YouTube, Apple, and everywhere else you listen to podcasts every-other Wednesday morning. It’s your new favorite source for the strangest science-adjacent facts, figures, and Wikipedia spirals the editors of Popular Science can muster. If you like the stories in this post, we guarantee you’ll love the show.

FACT: Breastfeeding backwash is a lot better than it sounds

Yeah, yeah, Rachel has a baby now and you all have to put up with learning mind-blowing facts about the miracle of childbirth. Boo hoo hoo etc.

But seriously: have you guys heard about baby backwash? It turns out that nursing isn’t a one-way street.

More scientifically referred to as retrograde duct flow, this is the mechanism by which breastfeeding babies shoot spit into the nipple of whomever is nursing them. When an infant suckles, they use their tongues to create a vacuum and hoover milk out of the milk ducts. But that motion also creates negative pressure, which pulls some milk—and saliva—back into the breast. First caught on ultrasound, this phenomenon has since been confirmed using MRI studies. (Side note: Definitely check out the adorable photos of babies getting prepped to nurse inside MRIs.) 

You might be wondering why this happens, either because you’re curious about its evolutionary purpose, because it fills you with visceral horror, or both. One possible answer is that this mouth-to-milk-duct communication pathway helps nursing parents produce helpful antibodies for their babies. We know that breastmilk carries more antibodies after a baby is exposed to illness, but it’s still not entirely clear how the lactating person’s body gets cued to make those changes.

The connection between breast backwash and antibody production hasn’t been proven in humans yet, but there are some promising animal studies on the subject—fortunately mouse pups are also guilty of backwashing.

Of course, as anyone with a baby (or who’s spent time anywhere near a baby) can tell you, a kid doesn’t have to shoot spit into your milk ducts to expose you to their germs. Between snot, sloppy kisses, spit up, poop and grabby little hands, there are plenty of other pathways by which a lactating parent’s body could get information about what antibodies to put on the menu. It’s quite possible that there are multiple inputs the body uses to accomplish this milk calibration, including one involving signals sent to a parent’s gut.

So what does this mean for parents who pump and bottle their breastmilk, either occasionally or exclusively? We can’t be sure, but there is evidence that milk straight from the breast has some unique characteristics that could be beneficial. But take it from this pumping mom: the research is clear that fed is best, any amount of breastmilk is great if you can manage it, and that the health and wellness of an infant has to do with way more than just how you feed and water them. Listen to this week’s episode to learn more about why breastmilk is such an evolutionary superfood and why we also should all try to calm down about it.

FACT: Solar eclipses cause mysterious communication chaos

Featuring Emma Gometz

This week’s episode featured special guest Emma Gometz, who works on Scientific American’s fascinating newsletters. She shared some facts about the bizarre relationship between the moon and radio communication. 

During the 2024 eclipse, NASA recruited ham radio operators to collect data about how radio signals behave during totality. Why? Because eclipses mess with the ionosphere—the layer of charged particles in our atmosphere that radio waves bounce off of.

But what’s really wild about this story is that, while eclipses create particularly mysterious disturbances in the ionosphere, radio waves actually travel differently whenever the sun isn’t out. So at night, you can tune into random stations that literally aren’t accessible to you during the day.

Tune in to this week’s episode to learn more about the moon’s mysterious impact on radio and how ham enthusiasts helped scientists test it.

FACT: A gender-bending squirrel once helped American soldiers get through wartime

By Sarah Durn

This week’s episode also features PopSci’s own Sarah Durn, who hosts our sister podcast Ask Us Anything. She joined us to tell the tale of Tommy Tucker, a dress-wearing squirrel who took the nation by storm. Just a few months into World War II, Tommy was rescued and adopted by a little girl who eventually passed him on to a neighbor named Zaidee Bullis. Bullis saw something special in Tommy and proceeded to make him a star. She sewed him some 100 costumes and took him on hospital field trips and other outings to support the war effort. Tommy was profiled in LIFE Magazine and apparently meant quite a lot to soldiers overseas. 

And yes: because Tommy’s tail would have interfered with trousers, he was dressed exclusively in skirts.

(If Tommy sounds familiar, you’re probably thinking of our previous episode on America’s pet squirrel craze!)

Now that you’ve thoroughly fallen in love with Tommy, check out Ask Us Anything to learn about how squirrels manage to keep track of all those nuts!