Vibrate a dish of liquid vertically and, above a threshold amplitude, the flat surface becomes unstable and breaks into a standing pattern of ripples. This is the Faraday instability, first described by Michael Faraday in 1831, and it is what is actually happening in every water-on-a-speaker video, whatever else is claimed for them. The description gives a neat way to think about it: in the frame of the oscillating dish, the fluid is sitting in a gravity field that varies in time.
The second half shows the more surprising result. Set the drive just below the instability threshold, so the surface stays flat, and a droplet of the same liquid placed on the surface will not merge — it bounces, generating waves it then interacts with, and starts to travel across the dish.
These walking droplets are often presented as a hydrodynamic analogue of pilot-wave quantum mechanics. The bouncing is real and well documented; how far the analogy extends to actual quantum behaviour is contested among physicists, and later replication work has narrowed the claims considerably. Watch it for the fluid mechanics.