What does the expression pack with the neck stretched out mean?

The expression pack that stretches the neck is to look back quickly. Watermelon video: These are some jokes that some young people are telling. For example, a beautiful woman came behind, and everyone twisted their necks at the speed of light, just to let everyone turn around quickly, and that beautiful woman came. Sometimes it is also a way of teasing, so that everyone can do one thing at the speed of light, that is, hurry up and don't waste time. "