a cloven hoof
An evil or malicious nature. The devil is typically depicted with cloven hooves. I thought I could trust Eric until he showed the cloven hoof by spreading rumors about me. Jill definitely sabotaged my last two relationships. She might seem nice, but she always shows a cloven hoof eventually.
a cloven hoofa symbol or indication of evil.
Traditional pictures of the Devil show him with the head and torso of a man but the legs and cloven hoofs of a goat. Therefore, a cloven hoof is a giveaway sign of the Devil.
1959 François Mauriac A Woman of Pharisees She had been a trial to him from the beginning, and now the cloven hoof was beginning to show.