Sharp Horsemanship

Great explanation of the worry cup

TRIGGER STACKING

A very important concept for riders to understand. Many spooks, bolt, buck or rears are a result of trigger stacking.
Trigger stacking is seen when a number of stressors or stressful events occur at the same time.
It's up to the rider to read the horses body language. Gain focus and relax the horse before his threshold is reached.
An example below.

Sam had a great lesson today. Nice relaxed horse and rider. Today she was practicing not using her reins and just using her seat and legs and upper body to change speed and direction