The whales welcomed them into their pods, started shooting them with echolocation to figure out what they were, and then started shooting them with..… - James Nestor

They're able to see better with sounds than we are able to see with our eyes.

It's a hard thing to fathom, the concept that you, me, the birds, and the bees—all life that is and has ever been—came from a few chemical reactions on some ugly rocks a few billion years ago. Proposing such a theory... [e]ven 50 years ago... might have gotten you... ostracized by the scientific community.
That all changed in 1977 when... chartered a research vessel... to the Galápagos Trench. Corliss suspected that a... , was erupting on the deep seafloor... [A]t a depth of around 2,500 meters... ANGUS’s temperature gauge registered a... spike. After several hours, the team... developed the film. ...There was life..—crabs, mussels, lobsters, worms—all flourishing... The incredible pressure, 250 times that on the surface, kept the water from turning to steam.

Even if someone has a pulse-ox or... a monitor, you can breath in certain ways and instantly see what it does to your body.