Earlier this week I got an insatiable hankering for a hard-boiled egg with salt and pepper. I loaded my saucepan with water and grabbed a good five or six eggs from the fridge. Not too long later I was happily munching on a mouthful of hard-boiled egg goodness.

But then the business of the day kicked back in and I had to throw the rest of them in the fridge and run out the door. I’ll usually make a point to set them in a different spot than the raw eggs, or to draw a little “H” on the hard-boiled shells. Not so this time. I just threw them back in and scrammed.

The time inevitably came when I stood with the fridge door open, studying the cluster of identical-looking eggs on their little shelf and trying to remember which side I’d put the hard-boiled ones on. My boyfriend must have noticed my scrunched forehead and puzzled look as I studied a couple side-by-side and held them up to my ear, shaking to see if maybe they sounded different. No luck.

“Spin it,” he said. My puzzled look must have remained. He grabbed the two eggs, readied them on their tips like spinning tops, and gave each a little twirl. One fell to its side and spun longways, the other stayed upright and spun vertically. He grabbed the one that stayed on its tip and handed it to me. “This one’s hard-boiled.”

I still braced myself a bit as I cracked the shell, but he was right. It must have something to do with the weight distribution of the raw egg versus the boiled egg.

There are a couple of versions of this spin test. The others I found have more to do with momentum—if you spin the egg and then try to stop it by gently pressing down with your finger, the still-spinning liquid of the raw egg will cause it to continue to rotate, while the solid state of the boiled egg will cause it to stop spinning all at once.

If all this spinning is making you dizzy, just remember to label or otherwise set aside your hard-boiled eggs to avoid getting them confused. Otherwise, all it takes is a little twirl to tell them apart.