After you watch enough knock-knock videos you develop a psychological dependence on them much like an emotional attachment to a public transit bus driver. Well, if you see someone day in an day out, anything can happen. What happens here is an interesting twist on the knock-knock theme centering on telephone chain-sex. Call the last person you talked to, screw them and pass it on. Torrid sex scenes, particularly Cheri Taylor doing it with Joey Silvera, overcome the gnawing realization you're listening to a lot of dumb dialog. A cute variation on a theme, now let's watch a half-dozen video companies beat this idea to death. Go on, I dare the first one —make my day.