In this video video Reddit user BuffPiggy says "It’s 10pm, watch what happens when you scream out of the window" He gets up, goes to the window and yells. Then you start hearing men, women - everyone in the surrounding buildings yelling back!

One version of the story as to why this happens says that the screaming was started in the 1970s by a student that lived in Uppsala's Flogsta neighborhood . They say he would let out stress from exams at 10pm and would yell out of the window. It actually has a name, it's called the "Flogsta Scream."

Some say the screaming started in honor of a student that committed suicide and would never let off steam. No one knows for sure, but I kinda hope it's the first one, cause the latter is kinda creepy.