An alliteration is a common poetic device that occurs when adjacent or closely occurring words have the same initial sounds or letters. Thomas Gray's "Ode on the Death of a Favourite Cat, Drowned in a Tub of Gold Fishes" contains several alliterations.
One example of alliteration in this poem occurs at the end of the second stanza—"she saw." It is a short one, but it still has a poetic element and foreshadows the ensuing events of the ode.
More alliterations occur in the fifth stanza. When describing how the unfortunate cat is unaware of the danger it is in, the poet says that
she stretch’d, again she bent,
Nor knew the gulf between.
Once again, there is a repetition of words beginning with s. Although the words nor and knew begin with different letters, they begin with the same sound and therefore are also an alliteration.
Later in the fifth stanza, another alliteration can be found. "Some speedy aid to send" contains three words beginning with the letter s.
The last two lines of the poem each contain alliterations.
And heedless hearts, is lawful prize;
Nor all that glisters, gold.
Once again, the poet has used the repetition of sound to add to the poetic quality of this piece.