Toilette paper has a resting heart rate of 81 beats per minute. At least, it does according to the Xiaomi Mi Band 3, a fitness tracker.

Here’s Jennings Brown, writing for Gizmodo:

As Chinese tech site Abacus reports, toilet paper is having a bit of a viral moment in China after fitness tracker owners discovered the Xiaomi Mi Band 3 would display a heart rate when attached to a roll. Users of the social media platform Weibo posted numerous images documenting the phenomenon. They also tested other cylindrical objects, such as bottles, cans, and even the appendage of a stuffed animal—all of which showed the mysterious phantom heart rate.

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Here’s a video from Abacus News showing this bug in action, using toilette paper, a banana, and a mug:

So what’s going on here? Fitness trackers use green lights to track bloodflow, because blood absorbs green light. So does toilette paper, it turns out, leading to this and other false positives.

Does this matter? Not at all: the devices still work as advertised on human arms, they just can’t tell the difference between humans and inanimate objects. This isn’t important, but it is hilarious. It also points a little toward how these devices monitor heart-rates. Give it a shot at home, if only to fool your kids into thinking everything is alive.