Last night was cold and clear, leading to an attractively frosty morning. The water in the bird bath froze, and somehow a tiny ice vase formed. I'm not sure if it grew by addition of layers, like a Bermudian Boiler Reef, or if it somehow rose/was squeezed from the water as it froze. It was about 2 cm end to end.
A mystery. And the coolest H2O-plus-cold-related phenomenon since the self-dinting snow of 2008.