It goes into the other hide when you leave the room.... ha ha....unless you watch it 24/7....

Arrange some substrate so that if the snake goes into and out of the 'unused' hide, you will be able to see its tracks. I had a ball python that appeared to be motionless for over 2 months. The only way that I knew the snake moved was because the substrate would get distrubed at the entrance of the other hide.