If I may loosely interpret what Tim is saying here, a keeper's aura, - the actions and energy projected, in other words body language - can cause a snake to act defensively (perceiving a threat) or calmly (no threat present). Basically "if you act like you're going to be bitten, you're probably going to be bitten." Nervous keepers tend to make choppy, grabby, quick movements that put a snake on edge. Staring a snake directly in the eyes for extended periods of time can also be perceived as a threat by the animal, especially among species with greater visual acuity. Calm keepers tend to be firm and deliberate in their actions, and go about the business of handling a snake without causing the animal undue stress or alarm.
Another tip for nervous handlers - eat a breath mint or chew gum. Both mask the scent of adrenaline on your breath, and also give your mind something else to focus on in the background.