It was once believed that all animals, having no soul, work like a simple clock.
A dog for instance - you pet it's head and it wags it's tail. You pull it's tail and it barks.

That theory has been of course proven to be wrong.
People, however, soul or no soul, are like that sometimes.

Buttons and levers.
Push the right buttons and you get a certain response.
Every person is the sum of his biology and his memory. The memory and brain structure define the personality.  Sometimes it seems as though the person himself is not in control at all, led by his impulses.