Ryan Reynolds warned Blake Lively that 'The Shallows' would "beat [her] up emotionally".
Lively appears in every frame of the horror movie, in which she plays a woman trapped on a rock in the middle of the ocean as a shark circles her, and after undertaking a similar project of his own in 2010's 'Buried', her husband told her she needed to be ready for a very tough experience.
Blake recalled him telling her: "This is going to be an athletic event. Prepare yourself. It will beat you up emotionally, it will be rewarding. It will be the most physical thing you've ever done in your life. Don't be thrown by that."
Despite undertaking a marathon movie of her own, Blake - who is expecting the couple's second child, a sibling for their 19-month-old daughter James - admits she wasn't particularly impressed by the premise of 'Buried', which saw her spouse trapped in a box buried underground.
She said: "I remember when I first saw that movie. I thought, 'I really like you, you're a cool person but I don't think I want to watch anyone in a box for an hour-and-a-half.' But it was beautiful film-making."
And it seems her shoot was as tough as the 'Deadpool' star warned her it would be because of the ferocious ocean waves.
Blake told Marie Claire magazine: "You don't even hear your director most of the time because there are waves you can't hear over. So we would sometimes do 16-minute takes, as long as we could, just letting your imagination take you wherever it could go."
The film's survival theme has seen it compared to 'The Revenant' - which finally scored her ex-boyfriend Leonardo DiCaprio his first Oscar - but Blake insists her mind was more focused on making a "cool and fun" movie than trying to win awards.
She said: "That's a very generous comparison. It's an isolation movie where, for better or worse, you have to hold the screen for 99 per cent of the movie.
"You're trying to make it a fun, sexy, cool summer movie. You don't have the pressure of trying to win your Oscar."
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