"Mary Had a Little Lamb"
From Tardis Wiki, the free Doctor Who reference
"Mary Had a Little Lamb" was a poem on Earth, written before the 20th century. The poem went:
"Mary had a little lamb, its fleece was white as snow, and everywhere that Mary went the lamb was sure to go."
In 1877, Thomas Edison recited "Mary Had a Little Lamb" to test his phonograph, making it the first audio recording ever.
The second voice somehow became trapped on Edison's recording, and was able to take over people's bodies by reciting the poem, transferring between bodies and tape. (AUDIO: Ghost in the Machine)
Behind the scenes
The Master's speech during the ritual to summon Azal in The Daemons is "Mary Had a Little Lamb" spoken backwards.
