frame damage. how did this happen?

[aznanimekid]

so i borrowed my brothers USP again today and when i went to clean after i'd finished i found his frame damaged. this was not here the last time i borrowed it and i was the last person who touched it before today. anyone speculate how this happened? i'm kinda stumped myself.







and yes i know, its mostly cosmetic. not looking to fix it just trying to figure out how it happened lol.

[Bug Splat]

Looks like the spring took a bite out, thats my guess. Is the spring the flat kind? There my be a bur or sharp edge on one of the coils.