XPS 15 9530, strange transparent white ball found in the case

Dear community,

I opened my laptop case for the first time, in order to clean up the fans. When I reassembled it, I this small transparent plastic ball (c.f. the picture) dropped off the case. I have no idea what it is nor where it came from. I don't think it is very important, but I'd rather know what it is.

Any clue?