Blake Lively's character Nancy Adams was put through hell in The Shallows, but it turns out the actress herself didn't come out unscathed. While it's true that successful Hollywood performers generally live lives of luxury outside of work, that doesn't necessarily mean the work itself isn't stressful. It can take a lot of mental energy to get into the right headspace to inhabit a role, and beyond the mental, days on set can be grueling 12-hour plus marathons, especially for the lead actors that are required to be in almost every scene.
In The Shallows, Lively was literally required to be in every scene, as for 90% of the film, she's the only human character onscreen. The premise sees a surfer named Nancy, grieving the recent loss of her mother, head to a secluded beach that her mom went to back when she was pregnant. What was meant to be a day of fun in the sun and remembrance ends up becoming a nightmare when Nancy inadvertently crosses into the feeding ground of a large, hungry great white shark.
For obvious reasons, Lively wasn't actually sharing the water with a shark, as the creature was instead created with - pretty good looking - CGI. However, that didn't prevent her from sustaining a real life injury during filming.
How Filming The Shallows Injured Blake Lively for Real
Near the end of The Shallows, Blake Lively's Nancy is clinging for dear life on a buoy. The shark charges and attacks, and Nancy gets knocked off. She quickly scrambles back onto the buoy, but while pulling herself up, smacks her face into the metal structure, complete with bonking sound. From then on, her nose is visibly broken and bloody, and there's a large gash on the side of her face. It turns out her face hitting the buoy wasn't scripted, and the injury as seen in the film and Lively's reaction to it were real. After the fact, it was decided that it fit the scene, so the footage was left in.
Lively's nose was really busted and bleeding for the remainder of Nancy's climactic battle with The Shallows' great white shark, but she gamely kept filming. Thankfully, her nose healed, and the result was an injury that only served to elevate the realism of the sequence, and make things more harrowing for the audience. Normally, these kind of unintended scene improvements during filming are seen as "happy accidents," but one doubts Lively was really that happy after sustaining what could've easily ended up a more serious blow to the head.