"She's so easy to act with," Rob tells E! News. "It's the first time since I've been doing acting that I've felt completely unself-conscious, because I could feel that she wasn't at all. That completely rubs off on me."
That's not the only superlative the Twilight hottie had for the girl who plays his little sister.
"She's phenomenal," he continues. "On the first day I met her, me, Allen [Coulter, the director] and Emilie were sitting around discussing our scenes together and she hadn't really said anything. I kind of asked just to be nice. I was just like, 'So what do you think about it?' And she's sitting there and goes into this whole diatribe about her character's backstory in the most interesting way. And she'd been writing notes on all the stuff we were saying and was quoting what we were saying back to us."
"She's incredible," Emilie agrees, admitting that she and the child star have remained pen pals over email. "She's just amazing in the film and she's a very, very smart girl. You can just watch her and you can forget what you're meant to be doing."
So could she be the next big child star like Rob's New Moon pal Dakota Fanning?
"She's going to be a massive actress, I think," he says. "She's the best improviser I've ever met. You can literally say anything to her and she'll completely stay in character."
And yet, much to Rob's surprise and chagrin, the Nurse Jackie starlet is still totally a kid.
"She's this hyperintelligent, hypermature kid, but I saw her play, and she's like a little girl when you see her with her friends. I don't understand how that happens at all."
"There's something about her—one of those indescribable things," Emilie says.
Pattz isn't the only one moving on from the vampire series. Check out our Life Beyond Twilight gallery.