In the office there is a candy box, supplied by Glico. It has a frog on top, and every time you take something from the box you put 100 yen in his mouth, then a woman comes to collect the money and replenish the contents a couple of times a week.
The snacks inside change all the time, but my current favourite is this "Mental Balance" chocolate, which claims to provide support in times of stress. I can't read enough Japanese to work out just how this is meant to happen, but since work is quite stressful most of the time it's nice to be able to justify eating lots of chocolate!
Update: Mari has explained more about the Office Glico boxes here.
