Photo: Entertainment Studios Motion Pictures

Thoughts on, and a place to discuss, the plot points we can’t reveal in our review.

While Lisa and Kate go about solving their various problems, a different sort of problem occurs to the viewer, who can’t help but notice that both women are due to run out of oxygen before the movie is even half over. Eventually, Modine’s captain sends down replacement tanks, saving their lives at the last minute. Why didn’t he just do that right away? Because he was worried that switching tanks might induce nitrogen narcosis. According to Wikipedia, this is “a reversible alteration in consciousness that occurs while diving at depth” and can result in “the impairment of judgment, multi-tasking and coordination, and the loss of decision-making ability and focus.” Other symptoms include “visual or auditory disturbances,” and the captain warns the women to keep an eye on each other, looking for signs of unusual behavior. As I noted in the review, any savvy viewer will tuck that admonition away for likely future reference.

And I was pretty sure that I’d identified the narcosis moment. About an hour into the film, Kate appears to be fatally chomped by a shark, with Lisa, who’s still trapped in the cage (her leg gets stuck when the cage is hoisted by a replacement winch and then that winch breaks as well), watching in horror. When Lisa subsequently makes contact via their intercom system or whatever it is (I’ve never done any skin-diving), I assumed that was akin to George Clooney showing up again toward the end of Gravity, and waited for Lisa to snap out of it and realize she’d been hallucinating her sister’s voice. But then Lisa frees herself from the cage, and finds Kate, badly wounded, and they swim to the surface, warding off sharks with flares (featuring a variation on the time-honored bit in which the hero takes a flash photo or lights a match and OMG THE SCARY THING IS RIGHT THERE INCHES AWAY), pausing to avoid the bends, and there are frenzied shark attacks as they reach the surface, and Lisa apparently escapes from a shark’s mouth by gouging out one of its eyes, okay sure, and all of this takes a long time, like, a good third of the movie, and finally, as both women lie battered but alive on the deck of the boat, wait a minute, things look hazy, the captain’s voice rings with static, and suddenly we’re back in the cage at 47 meters and Lisa is still trapped, and it turns out she hallucinated the entire third act of the movie. Which is admittedly kind of a bold reversion to stark realism (especially since Kate seemingly did get eaten by a shark), but I’m fairly confident that while nitrogen narcosis might cause you to see something that’s not really there, it doesn’t cause you to dream up detailed, lengthy action sequences, complete with jump scares and a false lull.