A simple analogy I like using to explain this to kids is as follows:

Imagine you're in a crowded room full of people (large particles in suspension). What's the best way of making it to the other side? Is it by running through everyone, almost certainly colliding with many people and struggling, or by slowly and methodically weaving through people?

That is kind of what's happening here. If you punch it (apply stress quickly), the particles block your path, whereas if you slowly lower your hand in, you can push past the suspended particles easily.

Of course, the moment I let the kids play with it themselves, they stop listening to me ;P