You never know where an idea will come from. This one came from a book of transcripts from Melvyn Bragg’s  BBC Radio 4 programme ‘In Our Time’. If you don’t know the show, it’s essentially Melvyn and a hand picked panel of experts shut in a small room with a microphone dissecting a different randonly chosen academic subject for 45 minutes live on a Thursday morning. One show might be about string theory, the next about the fall of Constantinople, the next about Mary Shelley, and then one about the Dreyfus affair. This show was about the origins of life, and Richard Corfield (I’ve spelled his name incorrectly in the strip) mentioned this fact about cat litter in it.  You can listen to the show here: http://www.bbc.co.uk/programmes/p004y29f. And then you can go through the archive – there’s over 500 shows there dating back to the first edition in 1998.