Collector: I would write "don't tell him this is here" on his forehead, hopefully nobody will tell him, then he'll see it next time he looks in the mirror and wonder how long it's been there. Possibly even a few days later if I'm lucky.
Astra: *looks at the Collector with a concerned face*
Collector: what? It's a harmless prank.
Astra: I'm just surprised you thought THAT far ahead for a prank. I'm not quite sure what I'd do, but it would probably be something he'd see when he wakes up.