Look, when it comes to zombies you really need to know what you're dealing with.  Zombies are excellent judges of character.  For instance if a human is the type to run away screaming, (that'd be me) you need to pick up a shovel and put up one hell'uva fight ( I could give it a go), or you can just faint dead away as it lumbers closer and closer.  They eat enough humans so they tend to get good at picking out the little faults of human behavior.  Guess you could attribute that to their success at catching slower humans off guard.