In his book Building a Church of Small Groups, Bill Donahue relays a story from his time as a part-time youth pastor while attending seminary. He was visiting a farm where two of his students lived, and their father decided to teach Bill a lesson:

He asked if I could help call in the sheep. I enthusiastically agreed. Sheep-calling was like preaching. We stood at the pasture fence, watching 25 sheep graze.

"Go ahead," he dared me. "Call them in."

"What do you say?" I asked.

"I just say, 'Hey, sheep! C'mon in!'"

No sweat, I thought. A city kid with a bad back and hay fever could do this. I began in a normal speaking voice, but Tom interrupted. "You are 75 yards away, down wind, and they have their backs to you. Yell! Use your diaphragm, like they teach you in preaching class."

So I took a deep breath and put every inch of stomach muscle into a yell that revival preachers around the world would envy: "Hey, sheep! C'mon in!" The blessed creatures didn't move an inch. None even turned an ear.

Tom smiled sarcastically. "Do they teach you the Bible in that seminary? Have you ever read, 'My sheep hear my voice, and I know them, and they follow me'?" Raising his voice only slightly, he said: "Hey, sheep! C'mon in!" All 25 sheep turned and ambled toward us. Tom seized this teachable moment.

"Now, don't you ever forget," he said. "You are the shepherd to my kids."