The film is set on a farm in Ireland and Emily admits they both had to take a ton of antihistamines to avoid falling ill during production.
"Jamie Dornan and I are both wildly allergic to farm animals, so I feel like any scenes where we were with the animals, we were dozily wondering around on too much Benadryl (allergy medication)," she told U.S. talk show "The View". "We were antihistamined (sic) up to our eyeballs at all points."
However, the "Mary Poppins Returns" star accidentally caused Jamie to suffer a nasty reaction after trying to help him look his best during his close-ups - when she forgot she had been touching a horse.
"There was this scene where I'm holding the horse and I'm talking to Jamie, and I noticed this rogue eyebrow hair dropping down, right before his close-ups, and I said, 'Ooh, I'll just fix your eyebrow for you,' and then, within moments, his whole face had just turned into this red monobrow of hives! No amount of antihistamine is going to solve Jamie's hiving problem around horses."
Laughing at how the pair had managed to land the roles, she quipped, "It was absurd that we're playing farmers and we're wildly allergic to anything to do with a farm!"
"Wild Mountain Thyme" is the big screen adaptation of John Patrick Shanley's play "Outside Mullingar", which is set in the Midlands region of Ireland.