At first I was thinking about how it it impossible to pull a string taught. This is because a string can not pull sideways, and eventually that is the only direction left to go, if it wants to be straight.
But this didn't really feel like a cool video. A string... yeah, and?
So eventually I ended making it about bows, because the same mechanism enables a bow to shoot very fast.
Funnily enough there are a lot of comments asking what happens if you shoot an arrow in space because I said "weight" instead of "mass"... oops! You live and you learn.