This happens quite often at my one chain of theaters here.
They have those sound-proof "cry rooms". These are rooms for families with little ones, so the grown ups can see the movie without disturbing everyone else with fussy little ones.
Its set up just like the rest of the theater except its in the back behind a glass wall. Take this (sound-proff), mix in a dark theater and add the fact that this theater's seats recline all the way back, I am willing to bet that there are a lot of "fooling around" going on back there.
