What are the list of things 당신 can do with a stop-watch? LOL

In season 1, episode 8, "They keep killing Suzie", at the end of the episode Ianto said "There's a lot of things 당신 can do with a stop-watch.", probably sexual things because of the looks he and Jack shared.
I was just wondering exactly WHAT can 당신 do with a stop-watch. Even my sick mind couldn't figure THAT out.
Do 당신 have any idea? XD