It's a little like casting out hundreds of fishing lines into the audience. You start getting little bites, then more, then you hook a few, then more. Then you can start reeling them in and that's a loveliest feeling - the whole audience laughing with you.
I also assume that they are not simply the physical properties of things as now conceived by physical science. Instead, they are ecological, in the sense that they are properties of the environment relative to an animal.

