It all started with a mis-hearing. Somebody mentioned the "gibbous moon" - gibbous, being from the Latin for "hunchbacked", is a moon between first and third quarters, but not full. Some of the more impressionable Beaker Folk thought they'd said "gibbon moon". And from this came the belief that the moon is inhabited by a divine gibbon, which eats the full moon every month, and then vomits it back up.
At times of proper, full-scale, meaningful lunar eclipses, the full moon goes a ghastly red colour. At these times, the Moon Gibbon Folk believe, the Moon Gibbon has launched an all-out attack on the other denizens of the moon, and our nearest neighbour is running with Clanger blood. If you don't know what Clangers are, this should help.
For we Bedfordshire people, a "clanger" is also one of these, eaten by field-folk in the 19th Century and, to this day, on special occasions.
The gibbon-gibbous confusion has caused much upset for the Beaker People in other ways as well. For example, a confusion over the term "waxing gibbous" (i.e. a moon on the way to Full) ended up with shivering primates all over the place. We try to discourage this kind of behaviour. But, notwithstanding various schisms, the Moon Gibbon people are still with us - and still get stroppy and worrisome as we near New Moon every month.