My cats like to lift their tails and shimmy them, like they would if they are spraying, but they do not spray. I think it is when they are very excited. One day out of the blue, Sterling did this an a bit of urine came out. I was flabberghasted!!! but he never it before and he never did it again, that is why I think it could be an accident.
The product feliway is a terric product for this type of behavior.. You may want to try that.