These were a weird thing that happened during the freeze.
We have a rather untidy and unlovely old plastic garden table top adorning our back terrace, waiting for us to find a way to transport it to the tip, where it's legs have gone before. One of the reasons it's difficult to move is that it was left upside down, thereby forming a series of pockets which have filled with a not insignificant volume of rainwater, which makes it very heavy. When this water froze a series of inverted icicles were formed, pushing up out of the pockets of water. We'd not seen such a thing before and can't really explain it, except perhaps it was something to do with the differing rates of expansion/contraction of the ice and the plastic surrounding it which caused the latter to push the former out of shape, or something.
Rather odd, and somewhat fascinating.