That's instinctive...they're at risk from a predator making a meal of THEM when they're in the middle of swallowing a meal- being out in the open puts them at much greater risk- that's why. Some snakes (like bull snakes) are more active hunters, but BPs prefer to ambush- they stay safer that way. So "play along".
Snakes are nowhere near as brave as horror movies would have you believe, lol.