It turns out our clever old bodies are able to do us quite a big favour when it comes to staying alive underwater for a prolonged length of time.
Recent reports of an Italian teenager who fell into a canal in Milan is the latest example of a miracle drowning survivor.
The 14-year-old reportedly drove off a bridge into the canal and never resurfaced. Apparently his foot became caught and it took nearly an hour to free him.
He is said to have remained on life support for a month but is now doing fine. So, how did the boy survive?
First, there's the diving reflex. It's a physiological response that has been observed mostly in aquatic animals but it has also been known to occur in humans. It's the same reflex that newborn babies have.
Babies up to 6 months old whose heads are submerged in water will naturally hold their breath, while at the same time their heart rate drops. The body pulls blood away from the extremities and other not as essential organs, helping them to conserve oxygen.
Another explanation is the selective brain cooling hypothesis.
It's a fact that the quicker the brain cools, the more likely it is to survive. So, if you're immersed in cold water for a long time, your body could retain carbon dioxide as a result of not breathing which causes blood vessels in your brain to dilate. This means more cool blood can enter the brain.
While it's hard to test both of these theories in an experimental scenario, brain cooling is considered a more likely justification for how the brain can be protected for long period underwater.