Game characters will actually do a dance in which they twist and contort their necks, backs, arms, and legs in ways which would be either very painful or impossible in real life, but which allows the game to have an ESRB T rating whilst still creating the illusion from the partially-obscured woo-hoo-capable object are engaging in something closer to a more realistic sexual position.
In the Simlish language, the term "woohoo!" is used more or less the same as in English, to denote sudden pleasure or pleasant shock. In-game, the act and phrase are both accompanied by the couple making noises, including cat shrieks, dog barks, truck horn noises, and even a female orgasm purr; usually accompanied by magical chimes to indicate pregnancy.
In the world of the game's community, the term has taken the place of "Play in Bed," a term borrowed from the original Sims that did not cause pregnancy in that game. Unlike the original Sims, Sims 2 partners will only woo-hoo in their underwear, unless a hack is applied telling them to do it in the nude. Such hacks are only now available on adult subscription sites.
The related sexual content to the "woo-hoo" feature has been the cause of much controversy, as there is argument over exactly how much sexual content is appropriate in a T-rated game.
"Woo-hoo"-ready objects include the Love Tub, any double bed, and most cars, as well as changing rooms in the shops.
The term was further popularized by its use in the seventh episode of The Strangerhood by Rooster Teeth Productions, where Catherine offers to bang Dutchmiller using the term.
Guy: "Oh. That just means that those two Sims want sex."
Gal: "But they're not even in love, let alone married!"
Guy: "That's because I installed LizzLove's Swinger's Bed Hack when you weren't looking, now they'll woo-hoo just as long as they're of legal age."