As long as your cat is on the bathroom door you might never find out.

You know when your cat stares intently into thin air? Or is chasing and batting around nothing? That's the greebles.

A greeble or unidentified house phenomena (UHP) are mysterious unexplained invisible and inaudible occurences that only cats seem to be able to see. Although many scientists have speculated on them, ancient aliyums researchers suggest that they might be the spirit of ancient aliyums (Xenu) trapped in our dimension.