The 44-year-old actor co-stars with Aniston in forthcoming movie Just Go With It, and said that he didn't expect her to be so quick-witted.
He told Access Hollywood, 'I couldn't believe how quick and funny Jennifer is.
'I know she is [funny] in real life, but it was pretty amazing when we were together how much fun [we had] and how she added and ended up beating me in scenes. I'd walk back to the trailer saying, 'I gotta get some writers to help me'.'
And he admitted to sneaking the odd peek at the former Friends actress' slim figure.
'It's a beautiful, beautiful thing. Jennifer works hard, she eats right, you know, she does. She never snacks on the stuff I snack on,' he added.