Rachel McAdams worried about being trampled by buffalo on the set of 'To the Wonder'.

The 34-year-old actress - who stars alongside Ben Affleck and Olga Kurylenko in the Terrence Malik-directed movie - recalled how she and the 'Argo' filmmaker shot a scene in the midst of a herd and had to be on high alert.

She explained: ''It was a funny thing because it was like, 'Make sure you're ready to run at any moment because buffalo are fast.' You look at them and they seem so awkward - sort of like penguins. They don't look like they were made to run quickly, but they're like bears! They're really fast.

''I don't know if Ben and I look terribly relaxed in that scene because we're ready to bolt at any moment. But it was extraordinary.''

While it's notoriously tricky working with animals on film sets, Rachel, 34, revealed producers had food on hand to make sure the four-legged extras stayed within camera view.

She added to The Guardian newspaper: ''They bribed them with food. They drive a truck around that blows this horn so they all know they're going to be fed, so they all stick around for a while.''