Some bank in Kuala Lumpur is advertising with this video about "ooblek". Ooblek is a mixture of corn starch and water dyed green to resemble the eponymous substance from a Dr. Seuss story. It is a non-Newtonian fluid. You can read the dry explanation at Wikipedia, but basically it boils down to ooblek being resistant to sudden or violent contact and movement (it resists being sheared). But if one just stands on it, not moving, one sinks.
Note that the bicycle rider sinks, since he doesn't have the forceful strikes of footprints. Just walking probably isn't good enough either, one needs to strike relatively fast.
We used to play with this when I was in school or at various Super Saturday events at schools. The last time was probably 8th grade. In science class we were supposed to design a spaceship that could land on a planet entirely covered in Ooblek. Mine was some sort of hovercraft, but the teacher admonished me for also including a reservoir of bacteria in the design aimed at consuming the ooblek and converting it into water and other, less annoying resources. To allow for human colonization, obviously. Apparently interfering with an alien planet like that is a bad thing or something, which the teacher made note of.
Non-Newtonian fluids potentially have other uses, besides amusing children. Research is being done on using non-Newtonian fluids in ballistic armor, since it could potential stiffen automatically to resist bullets.