The pair play husband and wife in the new film and became so close during the shoot they are now social media pals.
At first, Manville loved Liam's late night notes, but she has since had to silence him - because he sends too many.
"He will not stop WhatsApping me!" she groans. "He's a famous bad sleeper, Liam, so he stays up late (in New York) watching crime dramas and reading and I'm in London, and he's often still awake at four or five (in the morning)."
"So he'll be sending messages to me while I'm asleep! It used to go 'ping!' and I thought, 'Oh that's Liam'. I hadn't until recently learned that you can mute somebody on WhatsApp. But I've muted him now. I didn't have the heart to tell him that though."