At extremely low temperatures, liquid helium can achieve a superfluid state wherein it flows without friction. This means that if you were to swirl liquid helium inside a glass and set it down, the liquid would keep moving for millions of years and even climb over the sides of the container. It can also dribble through the tiniest cracks.
The liquid helium is in the superfluid phase. A thin invisible film creeps up the inside wall of the cup and down on the outside. A drop forms. It will fall off into the liquid helium below. This will repeat until the cup is empty – provided the liquid remains superfluid. Photo by AlfredLeitner PD image
