"Sounds like the old experiment you can do with cornflour" -- 1980s_coder
+1 for ooblek reference, but is it really the same? In that liquid, it's the mechanics of the starch chains moving over each other (sliding or jamming) which is causing the behaviour --- seems to me that what is happening here is a sort of piling up of particles in front of a penetrating object, rather than any change in the inter-particle interactions?
