We were watching a TV show in which the characters can leap into one another’s worlds at will – but they are invisible to everyone else. When two of these characters who’d been flirting with one another for some time finally hooked up and made out, it was almost inevitable that someone was going to turn up at one location or the other and see the person making out with the air. It’s a joke too impossible to resist. We predicted the wrong location and the wrong observer but we knew that there would be an interruption of some kind. No one asked this question – the invisibility of companions had already been well established but – the seeing nothing was a funny something.