WTF is going on in the apartment across the street from me?

This happens in the apartment across the road from me every night:

The lights flash on and off over and over and over again for several minutes. Then the flashing slows down and stops and the lights stay on after that. Sometimes you can see someone walking around in there when this happens and sometimes not.

Does anyone have *any clue* wtf is going on over there? We can’t for the life of us think of any reasonable explanation.