If Joe Mazzello looks familiar, he should—just subtract 16 years and add a velociraptor. After starring in Jurassic Park, Mazzello, like a lot of other child stars, took some time off. Unlike most, though, he has reemerged.

[Read More on Details.com: The Child Stars Who Shaped Gen X]

He's now working with that Spielberg guy again, starring in HBO's much-anticipated 10-part World War II epic The Pacific as U.S. marine Eugene Sledge, whose 1981 memoir provided plenty of source material. For additional research, Mazzello completed a grueling 10-day boot camp in the Australian bush. "Everything kills you there—every plant, every animal. Even you yourself become toxic," he deadpans. "If you touch somebody, you'll kill them."

[Read More on Details.com: The Fallen: The Liberal Idealist]

Next fall Mazzello appears in David Fincher's The Social Network, playing Facebook founder Dustin Moskovitz. Some advice for costar Justin Timberlake: Don't stand too close.

[Read More on Details.com: Check Out Facebook's Pussy Palace]