Karl Georg Reutter II was appointed choirmaster at St. Stephen’s Cathedral in Vienna in 1738.  The following year he went on tour to recruit choristers.  In the town of Hainburg, Joseph Haydn (at stage seven years of age) auditioned.  The contemporary biography Guiseppe Carpani recalled:

Reutter gave him a tune to sing at sight. The precision, the purity of tone, the spirit with which the boy executed it surprised him; but he was more especially charmed with the beauty of the young voice. He remarked that the lad did not shake (trill), and smilingly asked him the reason. The boy replied promptly: “How can you expect me to shake when my cousin does not know how to himself?””Come here,” said Reutter, “I will teach you.” He took him between his knees, showed him how he should produce the notes in rapid succession, control his breath, and agitate the palate. The boy immediately made a good shake. Reutter, enchanted with the success of his pupil, took a plate of fine cherries and emptied them into the boy’s pockets. [According to Dies, he also gave Sepperl a piece of money.] His delight may be readily conceived. Haydn often mentioned this anecdote to me, and added, laughing, that whenever he happened to shake he still thought he saw those beautiful cherries.

Cited in: Geiringer, Karl (1946) Haydn: A Creative Life in Music.  New York: W. W. Norton, p.28.