If "Take a break" wasn't on your list already I would have suggested "Go for a smoke" :)

In fact there a psychological studies that indicate our brain is processing information unconsciously whenever we do something not using it (for which smoking I guess is a perfect example in more than one way:)). Whenever you experienced to got a new idea to tackle a problem while on the toilet or taking a shower or after gossiping with colleagues for some minutes it is for that reason. IIRC the ideas for the laser and the transistor were found during breaks.

So don't disturb those seemingly doing nothing of value. They may come up with the next "big thing" for Apple or something.