Posting will be light this morning as Professor Ceiling Cat has cat stuff to do. In the meantime, entertain yourself with two videos of a remarkable phenomenon of physics: the slinking chain. The first shows the phenomenon, and the second goes into greater detail.
A longer video:
If you want a more detailed explanation for this weird phenomenon, a long one (which also accurately predicts the chain’s speed) is given at Empirical Zeal. It may be more than you want to read, but at lest read the first and last parts. The answer involves changing momentum.