Invisible piss
When your pissing most usually on a toilet and the feeling of piss brushes a part of your body most commonly your legs or foot despite no piss actually making contact with any part of your body.
Brain: Dude stop pissing on your leg!
Eyes: There is no piss...
Brain: Oh I had just conducted Invisible piss!
Eyes: There is no piss...
Brain: Oh I had just conducted Invisible piss!