A long time ago I dated a girl who had a sort of bruise or rash on the back of her thigh. She had gotten it looked at but I guess it was nonspecific and benign, and so her doctor let it be.
Once, when I was out of town, she stayed over at my house for a long time— something like two weeks. The rash disappeared!
When she went home again, it reappeared!!
This kept happening. She would stay at my place for three or four days, and it would go away, but as soon as she returned home it developed again. The rash was always in the same general area and in the same shape. She bought new sheets, a new computer chair, and on and on, but it kept coming back. This happened until she eventually moved, and then it went away forever.
Man, that was like ten years ago and I still think about how weird that is. Why was this happening?!