Icy stare

Wednesday afternoon is "Cake Time". Everyone gathers in the recreation room and enjoys cake and talk to everyone. This time some people moved over to the foosball table and played for a while. It didn't take long before the head of my department looked in without saying anything and then leaving. Within seconds, everyone in the department said "I better get back to work." Of course, I followed suite, but I don't understand it. If the company wants us to relax and enjoy ourselves for a while, then why send the department head out to keep everyone in line?