"First of all, we needed to enable interactions between more than one 
entity. What do I mean by entity? Well, think about the ractives. Think about First Class to Geneva. You're on this train—so are a couple of 
dozen other people. Some of those people are being racted, so in that case the 
entities happen to be human beings. But others—like the waiters and 
porters—are just software robots. Furthermore, the train is full of 
props: jewelry, money, guns, bottles of wine. Each one of those is also a 
separate piece of software—a separate entity. In the lingo, we call them 
objects. The train itself is another object, and so is the countryside through 
which it travels.