Merlin's Mist
When a man is nearing ejaculation, his partner must say "Abracadabra" (or "Accio" for the Harry Potter fans) and tap the head of the man's penis with their index finger, or wand if available. Upon tapping, the man will ejaculate onto his partner's face creating Merlin's Mist.
Hermione cast a Merlin's Mist and Ron slept for the next 12 hours straight.