The song is from season 2 episode 13 of MLP:FiM.
♫ Lyrics for the song:
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[Pinkie Pie]

First you jiggle your tail! Oink oink oink!
Then you wriggle your snout! Oink oink oink!
Then you wiggle your rump! Oink oink oink!
Then shout it out! Oink oink oink!

[repeat verse two more times]