The knuckles of this Cumulonimbus capillatus incus cloud rapped against the sky over the River Thames in London, England. The features in the middle of the image, formed on the underside of the canopy, or incus, spreading out at the top of the storm cloud, were spotted by Ella du Breuil (Member 40,742). This was during a brief dry moment between showers during exercises as volunteers on one of the river’s Royal National Lifeboat Institution lifeboats. ‘Knuckles’ is a colloquial term that storm chasers use for these digit-like cloud features running down the edge of the cloud’s anvil-shaped upper region. They indicate that powerful updrafts within the Cumulonimbus are causing its anvil to spread out rapidly, expanding in the face of opposing high-level winds. They’re the storm cloud’s way of saying, ‘Speak to the hand because the face ain’t listening.’