You're set up for a heavy deadlift. You're nice and tight: your trunk feels like one piece, a strong, straight line. You taste the weight. This is going to be tough. You don't jerk the weight off the ground - a rookie mistake - liftoff is strong and steady. But crap, it's heavy. In fact, it's not really going anywhere. "Up," you think and lift your face towards the heavens. Suddenly your pelvis rounds, your straight line resembles an orange slice, and your lift crashes to the ground as your mouth lets rip a deafening "Noooooooooooooooooo!"
What happened? You chicken necked. Also known as cervical hyperextension. You gave away your nice, straight spine when your head went back. The neck is part of the spine, right? Right. The spine should be in neutral position when deadlifting, right? Right. So why give that away by throwing your head back? Chicken necking is not only wrong and unattractive, it opens you up to potential injury. Loss of neutral spine during a lift puts great stress on your spinal discs and can cause a herniation. So be kind to your back and keep your neck in check.
Chicken necking isn't limited to deadlifts. We see this in other lifts too. So stay alert: any time we say "straight back" or "neutral spine" - this means your neck too!