AceShowbiz - Director Jason Reitman has heaped praise on his "Tully" leading lady Charlize Theron, insisting she's one of the few actresses who can become a filmmaker's puppet while getting lost in a role. The moviemaker, who also worked with Charlize on "Young Adult", admits she's a joy to work with on set, because she needs very little direction.

"She's very vulnerable and she feels what her character feels," he told WENN. "Actors kind of fall into two categories for me. There are human puppets who are good at puppeteering themselves. You can describe what you need and then they puppet themselves to do that and they can be very good at that."

"And then there is the other group that are actors who are lost in it and they actually feel a character's feeling. Charlize actually is one of two actors I've ever met who is strangely both."

Reitman further raved about Charlize, explaining she'd get up in the middle of the night and eat just to gain weight for her latest role as a desperate mum.

"She's been asked about the weight a lot and the way she describes it is depression, having to eat all that food," he explained. "Just constantly taking it in and not having a relationship with her body. She would wake herself up in the middle of the night to keep on eating salty foods to keep the weight on."

"And this was right after (film) 'Atomic Blonde', by the way. It put her further into the character and deeper into what the character was feeling."

Charlize gained 50 pounds (22.6 kilograms) to portray overwhelmed mum Marlo in the new film, which hits cinemas on Friday, May 4.