Cat's paw

There is a term that has been used in employment discrimination case law to describe a situation where someone who decides to fire an employee acts upon recommendation of the employee's supervisor, and therefore acts as the conduit of the supervisor's prejudice - his "cat's paw." Does anyone know the origin of this phrase? Thanks.

Merriam-Webster online line says: 2. from the fable of the monkey that used a cat's paw to draw chestnuts from the fire. One used by another as a tool.