Waves of water travel down a flight of stairs making it look like a Water Slinky. 

"What walks down stairs, alone or in pairs
and makes a slinkity sound?
A spring, a spring, a marvelous thing!
Everyone knows it's Slinky.
It's Slinky, it's Slinky,
It's fun, it's a wonderful toy.
It's Slinky, it's Slinky, it's fun,
It's a wonderful toy.
It's fun for a girl or a boy!"