The Claws are an object that emerges from the ground when the ritual is done.
The ritual can be done by placing an item, and pouring white sand around the object while speaking the words. But a victim must be in a coffin underground, alive.
Episode 3 - Buried Alive
Caroline was the first victim, resulting in the artifact being concealed. Later, Justine was the second victim. By burying her alive, the curse ended up being reversed and revealing the hidden artifact. Both victims were unwilling, as the ritual states the victim must be to be buried alive
Dennis performing the white sand ritual