What is the purpose of the fox snake vibrating its tail rapidly against dry ground cover?

Answer

To mimic the sound made by a rattlesnake.

This specific tail vibration is an evolved defensive tactic designed to fool observers into believing they are encountering a dangerous venomous snake, specifically a rattlesnake.

What is the purpose of the fox snake vibrating its tail rapidly against dry ground cover?
behavioraggressionreptilesnakefox snake