Funny way of showing it.
Think about it this way. Their eyesight is poor. They are seeing lights and darks. To them, dark means safety and shelter. You come up on one and startle it, it’s going to run to the first cover it sees.... since it’s focused on you, it’s going to see the dark under you from the shadow under you. It’s going to go for that dark safe spot.
The key is not to panic. Most of the time, they’ll realize their mistake and keep on hauling right past you.
Venomous snakes rely on their venom to kill prey. It’s a last ditch defensive resort as it takes a lot of energy for the snake to produce that venom. They don’t just waste it on anything walking by. 99.999% of venomous bites in the US are purely defensive. People trying to kill the snake or otherwise harm it and the snake defends itself. Given how the mouth breathers like to have round ups, I can’t really say I blame the snakes when they do tag some of these idiots.