There's this thing you do with your throat that is called a "glottal stop", and it's what you do when you are sounding out a soft 't', like in mitten but not smitten.
Controlling this glottal stop is the key to opening your throat.
Have you ever went to the dentist for a regular cleaning, and the last thing they do is where they fill in 2 plastic molds with a cleaning foam, and it fits around your teeth so that the teeth are touching the foam the whole time?
Then they have that air vacuum wand that you put in your mouth and close your mouth? You can create a seal with your lips, and can open the nasal/throat cavity valve, so that the air vacuum in your mouth is sucking in air from your nose. It's kind of like that.
Could have been a camera trick, but it's quite possible if he's trained to open his throat. It's something that a lot of competitive eaters and sword swallowers learn to do where they can relax the esophagus and let it just drop straight down.
It's risky and can lead to choking and/or stomach problems if you aren't careful, so it's not recommended you try it.
Nah, it's only in large quantities. Like more than 3 liters within a minute or something.
The problem is when your intestines/liver and kidney can't keep up with "filtering" the water out of your system fast enough. Having too much water in your system creates areas of really low concentration solutions, which interferes with your body's natural exchange rates. Not only that but water by itself can dissolve/contact things it isn't meant to under normal circumstances so you end up having water "poisoning".
Basically, if you're drinking so much at once that you can't piss it out as quickly as you're taking it in, you're gonna have a bad time.
I've done 2 liters in like... 2 minutes, no adverse consequences. You just gotta piss.