Humpty Dumpty

Humpty Dumpty was an Earth nursery rhyme. Shortly before the Sontaran invasion of Earth in 2009, UNIT Private Harris told General Staal to "stop playing Humpty Dumpty". (TV: The Sontaran Stratagem)

Jo Grant recited this rhyme to counter the Master's hypnotism.

Behind the scenes
According to The Brilliant Book 2012, a book that contains non-narrative based information, the story was inspired by the Sontaran, Strax, when he met the Doctor.