Roosters can not be stopped once they start a crowing contest but they can be started! Just about anything can trigger them: a phone ringing, a car arriving, the dog barking, a clock chiming, the doorbell, a horn, another rooster, a text message alert, and the list goes on and on!
A rooster can only crow when his neck is fully extended. They do this roll their eyes back in their heads that are only slightly creepy. They close their third eyelid when they crow which only gives the appearance of an eye roll. Still slightly creepy.
Roosters have several different vocalizations. They have a clucking sound that says "come here hens, I found a treat" They growl at other roosters to threaten them, or keep them in line. They have warning sounds they make when they want to warn the flock of a hawk or other predator nearby. They also have their Velociraptor impression, but you have to see that one to believe it!