There's always so much to learn on TikTok, from life hacks and recipes to new dances and trends.
But now we can all thank one user for informing the world about the function of those 'spare' red bulbs that are sometimes found in packs of string lights.
TikToker @viznelly took to the video-sharing platform to demonstrate exactly what they do - and our minds are blown.
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With Christmas fast approaching, watch the video below:
In the clip, the TikToker showed off a string of Christmas lights hanging on a door frame, before holding up a red bulb - which many assumed to be a spare.
"I was today years old when I found out what these are for," they said.
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Moments later, they removed one of the regular bulbs from the string of lights that appeared to be turned off, and added in the red bulb instead.
"Wait for it," they added, before just seconds later, the lights changed.
People were mesmerised in the comments, with many struggling to understand how replacing the bulb could change the way the lights operate.
One person explained: "Old strings of lights come with an 'extra' light with a red tip. When you put it in for another bulb, it makes the whole string of lights blink."
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While another added: "The old string lights ran at a constant power supply, by adding the red globe that is made different, the power cuts in and out."
A third said: "As someone who grew up in the 90’s… I thought everyone knew this... We didn’t always have remote control lights!!"
Others were stunned that they never realised earlier, with one person commenting: "1000% thought they were spares. I have been robbed."
Another said: "I thought it was a tester to see what bulbs don’t work??"
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Meanwhile, someone else penned: "Dude all they had to do was write that somewhere on the box. I wasted so many years not knowing about this."
Some users, on the other hand, were shocked that people didn't already know this about the little red bulbs, with another noting it was 'common knowledge'.
"I used to put up the Shristmas lights at my parents house so I didn’t know that this wasn’t common knowledge," they said.
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And another commented: "I known for years since i was a kid, I'm 33 now."
A final user added: "Thought everyone knew this. We called them blinkers!"
Many modern Christmas lights these days come with remote controls or switches on the plug sockets, but at least we know what these little red bulbs do in case we ever come across them.
Featured Image Credit: TikTok/@viznellyTopics: Christmas, Life, Real Life, TikTok