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I think they exhale on the way to the surface. Something to do with the re expansion of the air in their lungs.

Only if you're on scuba gear, breathing compressed air. You're subjected to 14.7 psi of pressure at sea level. Your body is pressing out with the same amount of pressure, which is why you don't feel it. Now when you dive, water places a pressure of 44 psi per 100 feet, or roughly 1 atmosphere of pressure per 33 feet (we were taught 3 atmospheres for every 100'.)

So if you take a breath of air from a tank while at 100', the air in your lungs is the same pressure as the water and atmospheric pressure on your body; i.e., about 60 psi. If you were to ascend without exhaling, your lungs would eventually burst or undergo what's known as an embolism, where the aveoli rupture. Embolisms have been documented to occur in as little as 3 feet of water. The first sign we're taught to look for in embolisms is frothy pink (highly oxygenated) blood.

However, because she takes no equipment down with her and doesn't breathe air under pressure, it's perfectly safe for her to breath hold, dive, and come back up all in the same breath without exhaling.

That being said, it takes someone VERY in tune with their bodies to do something like this.

That being said, it takes someone VERY in tune with their bodies to do something like this.

My husband and son freedive (spearfish), but only to depths of about 40 feet. They have a friend who dives with them, and he's a serious freediver, 120 foot depths and he holds his breath for 4 plus minutes. But he's very aware of shallow water blackout and has taken classes (under controlled conditions) where they have you hold your breath underwater till you pass out, so you can know how it feels when it's about to happen.

Embolisms have been documented to occur in as little as 3 feet of water.

Can you document this, please?

Not calling BS, just surprised. What is the pressure differential over 1 atmosphere at a mere 1 meter's depth?

Cheers!