Yet another joy of living in a 100 year old house

I live in a triple decker. Three identical apartments stacked on top of one another in one really old (i.e. pretty sure there wasn't a shower inside when it was built) house.

Last night right as I was falling asleep I woke up because my bed was shaking. My room was shaking. I seriously thought we were having some sort of mini-earthquake. My roommate didn't seem to be worried- all quiet on that side of the apartment as far as I knew. A mini-Earthquake never hurt anyone so I decided to go back to sleep. Then, a few minutes later I woke up again. This time things seemed to be shaking a little more. Ok, now I was starting to get a little scared. I decided that if it got worse I was going to get worried and wake my roommate up. It calmed down and I drifted back to sleep. I woke up again to the quaking. This time was a little different. Now I could hear the movement of bed springs in sync with the shaking! Yes, someone in my house was having sex so vigourously that it literally shook the house.

This morning my roommate told me that her bookshelf was shaking last night. Good for them.