The girl's totem
When Iza turns up with a strange, wounded child, Creb is the one who decides what she means. The marks on Ayla's leg show that a cave lion attacked her and didn't kill her.
To Creb, that means the lion's spirit protects her. It's an unusually strong sign for a girl, and it helps convince the clan to take her in.
Creb's word carries weight. Brun is chief, but he doesn't ignore what his brother says about the spirits. By tying Ayla to the lion, Creb gives her a reason to stay.