Why did the angel of Yahweh tell Balaam about why his donkey acted the way she did?

The angel told Balaam that when his donkey saw the angel she turned away three times.

What did the angel say would have happened to Balaam if his donkey had not turned away?

The angel told Balaam that if his donkey had not turned away the angel would have killed Balaam and spared the donkey's life.