Look closer guys the head of that snake is not real it isnt even attached to the body :
OK, at 0.27 it does look like the snake's neck isn't attached at the body but...
0.16 - ...that's because the neck is curving into a loop
1.16 - you can definately see the loop here
I'm not well up on GTP's but I've observed corns drinking plenty of times and they DO move their mouths like that when they're drinking
1.56 - you can see the underside of the snake's neck moving as it swallows
2.32 - snake's head moves slightly, mine do this too
2.35 - air bubbles in nose as the snake exhales start to appear
4.07 - up to about now the tongue flicks were fairly uniform, regular and slow, but they start to change now
4.10 - tongue flickers rapidly when the snake sticks tongue out