Question

How could lizards cut off their tails when chased by a predator?

Answer 1

Tail shedding is generally called autotomy.
Autotomy occurs at specific areas of weakness – the tails are essentially "pre-cut". Often, there are multiple regions of breakage, allowing the lizard to lose only the minimum length necessary. Breakage simply occurs between adjacent vertebrae, a natural weak point. Lizards don't need any extarnal force to shed their tail. Active contraction of neighboring muscles contributes to breaking the fracture plane.