What’s a “normal” thing that feels totally weird when you really think about it

You ever do something totally normal and then suddenly realize how weird it actually is? Like… clapping. Why do we smack our hands together to show approval? Who decided that was a thing? Or how about blowing out candles on a birthday cake? "Happy birthday! Now exhale all over the food we’re about to eat!" What’s something totally normal that suddenly feels bizarre when you stop and think about it?