The actress explained how she had to stand in front of a green screen and use her imagination to act out scenes with scary wolf effects.
She tells US news show Access Hollywood: '[Cgi filming] is exhausting and probably the least fun part of my job. I say that because our imaginations are all we have in times like those, but I had to have this certain level of fear that is hard to get when you're not terrified. I had to trick my body into being scared and that was just exhausting.
'I hyperventilated, I [jumped] up and down, and [was] crying, and it's just really tiring, and I'm looking at a piece of wood. I wasn't getting anything. It was all in my head.
'We did have a Styrofoam wolf called Stuffy that was life-sized - he didn't really help that much!'