Most snakes are head-shy to some degree, although I have a few BPs who totally aren't... Toby actually leans into my finger, and lets me rub both the top & bottom of his head. The only way I can think of to make one less head-shy is just regular, gentle handling - but some will never get used to it. It also helps to approach them (with your finger) from the neck/back, rather than coming at them head-on.