Sequels are tough. "Here we go again!" so easily becomes "Here. We go, again." Characters start getting a little sick of each other, as they do in "Ice Age: Dawn of the Dinosaurs," with the story falling back on a falling-out between a mammoth and a sabre-toothed tiger, or the tiger and a sloth. The dialogue begins to sound like screenwriters voicing their creative frustration. "Face it, Sid," Denis Leary's Diego mutters to John Leguizamo's lateral-lisping mammal Sid in "Dawn of the Dinosaurs." "We had a great run, but now it's time to move on."

Not bad, not good, "Ice Age 3" may be OK enough to do what it was engineered to do, i.e., baby-sit your kid for a while and rake in the dough, somewhere in Twentieth Century Fox's preferred coinage realm of "Ice Age 2" ($651 million worldwide) or, more modestly, the first one ($383 million). Directors Carlos Saldanha and Michael Thurmeier and the four credited writers amp up the peril, if not the humor, of the first two. The mammoths, Manny and Ellie, are expecting a baby, and Manny's baby-proofing everything in sight. (It's the best gag in the picture.) Diego feels like the odd man out; he takes off on his own, while sweet, desperate Sid discovers three dinosaur eggs, which he adopts, thus drawing the attention of an enormous T.

In a strained science-fiction leap, "Ice Age 3" sends the gang beneath Earth's frozen surface, where they discover a vast "Land of the Lost"-type jungle realm, home to highly marketable scary creatures from the old days. The primary addition to the character roster, a swashbuckling one-eyed weasel named Buck, is theoretically entertaining -- always getting everybody into trouble, pulling off feats of derring-do right and left. I'm puzzled as to why Buck isn't more fun in practice, though, even with Simon Pegg providing a zesty Cockney vocal characterization.

Lack of comic distinction and defiantly forgettable computer animation have always held back the "Ice Age" projects. "Dawn of the Dinosaurs" lays out one life-and-death scenario after another, dutifully. The pileups passing for a climax find Ellie (voiced by Queen Latifah) giving birth; Manny ( Ray Romano) fighting dinosaurs; Diego battling his own set of adversaries; Sid navigating a river of molten lava; Buck piloting a flying prehistoric bird, accompanied by squabbling possums (Seann William Scott and Josh "Perpetually Annoying" Peck). No wonder the comparatively simple frustrations endured by the squirrel-rat hybrid Scrat (Chris Wedge) offer some relief. Also, I realize that with most "Ice Age" fans, puke, snot and mucus represent the trifecta of sight-gag comedy. Nonetheless: This movie has a lot of all three, and only a handful of laughs to show for its damp self.