Sue Cameron told us about this one, then Ron transcribed the Joni reference for us. Thanks!
She took a step backward to compensate, tripped over a rock, and sat down hard. Her jaws clicked together hard, with her tongue between them – exquisite pain! – and she stopped giggling as if the sound had been cut off with a knife. The very fact of her sudden silence – you turn me off, I'm a radio – seemed funniest of all and she began to giggle again, in spite of the fact that her tongue was bleeding, and tears of pain were streaming from her eyes.
(Contributed by Sue Cameron, Ron)