From Jerry Lewis to Eddie Murphy, the bottom-line rule of thumb in contemporary American film comedy has been that the more control a performer has over his movies, the less funny less daring, more self-indulgent they become. Not so Jim Carrey, whose fourth starring role, in Ace Ventura: When Nature Calls, is his best yet. Unlike so many superstar comics before him, Carrey has retained a raw hunger for The Joke the killer punchline, the ultimate sight gag that seems insatiable, and this gives his work a furious, omnivorous energy. Even when the jokes are as corny as this movie's subtitle is, Carrey regularly squeezes a laugh out of you through sheer force of will.
When Nature Calls finds pet detective Ventura in Africa, where he's in search of a rare white bat. Unlike his character in Dumb and Dumber, Carrey's Ace is all coolness and confidence he swaggers around the jungle with that hip-swiveling, John Wayne-on-joy juice walk, sassing everybody in sight. (Trust me: Kids all over America will be hitting you with Ace's new wise-guy catchphrase ''Spank you spank you very much.'') As always, the verbal comedy is nonsensical and vulgar, and the physical humor is rigorously conceived and really vulgar.
Ian McNeice plays the English diplomat who accompanies Ace on his bat quest, and Carrey's In Living Color cohort Tommy Davidson is terrific (and unrecognizable) as a battling member of the Wachootoo tribe. But mucus might just as well receive costar billing too, for all the gleefully gross screen time Carrey gives it. There's also a scene in which a mechanical rhinoceros ''gives birth'' to a naked Ace (sorry, the context is impossible to explain here) that would do Laurel and Hardy and Luis Buñuel proud.
Carrey and his writer pal Steve Oedekerk, making his debut as a director, are fearless in their spoofs of African-jungle-movie stereotypes. They get away with potentially offensive stuff simply: None of the black characters are stupid, or mere figures of fun. (Carrey works in a sweetly silly romantic scene with the film's only prominent woman, a tribal princess played by Sophie Okonedo.)
To be sure, When Nature Calls is very uneven and pretty much falls apart in the last half hour, but it's a heck of a lot of fun before that. Plus, Carrey is one of the few comedians I know of who, at the end of the 20th century, are resourceful enough to coin a fresh slang term for masturbation (for the record, it's ''practicing my mantra''). No, spank you, Ace.