When we hear a word such as 'shoot', our minds are instantly looking for who does the shooting and what has been shot. If the same utterance mentions a person and a bird, we would match the human to the shooter and the bird as being shot, even of the order is ungrammatical (e.g. "shoots crow man"). Each term has slots that need to connect to matching things, just like the pegs on Lego bricks. The same mechanism can be used in natural language processing alongside, or in combination with, more formal grammar.
Used on Chap. 14: page 332