They can launch quickly with their tails, but then they can't chase with speed or agility. The zig-zag advice is about the fact that they can't keep up and maneuver. I'm speaking from extensive personal experience. They are slow, lethargic and not aggressive during daylight. That video was actually a good example of the difference between crocs and gators. Gators don't aggress like that and they cannot move anywhere near that fast.