Jessica Biel goes green - literally - as a sassy, girl-next-door alien opposite Dwayne Johnson in the animated 'Planet 51,' in theaters Friday, and she tells ET that, like her character, she's been crushed by some high school crushes in the past!

"Probably every crush I ever had was something awkward like [in the movie]," Jessica tells ET. "It's hard to ask people out. It's hard when you really care about somebody -- you don't want to be rejected. I completely understand that. I think everyone has gone through some sort of rejection in that sense, and it's a bit of an ego blow. … I have been rejected plenty of times, my friend. Plenty."

'Planet 51' finds Dwayne as Captain Charles "Chuck" Baker, an astronaut who thinks he's the first person to land on a new world, only to quickly learn that the planet is inhabited by little green aliens who distinctly resemble the populace of 1950s America - and are paranoid of an alien invasion!

"It's about not having a fear of something you don't know about," says Jessica about the film's theme, "and being non-judgmental about someone who's different from you, or something that's changing in your life."

Since 'Planet 51' clearly believes in life out there, does Jessica believe too?

"I do," she says definitively. "Our universe is so expansive, I think it's kind of silly to think that we're the only beings experiencing life here."

Watch ET for more with Jessica and the cast of 'Planet 51'!