What are the danh sách of things bạn can do with a stop-watch? LOL – Liên minh huyền thoại

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