Question about the example

For the example of the project page, the patterns about "running" are as follow:

``` ruby
2.0.0-p353 :012 > running_things = @animals.describe([:running])
 => [:cats, :fish, :humans, :rats] 
```

Can you explain why the running_things include ":fish"? How does the associative memory learn that ":running" related with ":fish" in this example?

Thanks
