Why do you think Bilal (peace be upon him) was turning his face from side to side while pronouncing the Adhan for prayer according to the narration of `Aun bin Abi Juhaifa's father?
 Narrated `Aun bin Abi Juhaifa:                     My father said, "I saw Bilal turning his face from side to side while pronouncing the Adhan for the prayer."