This section is based on the physical phenomenon called the same. Here is a simple example concerning light: let us imagine a white coloured object (that is it reflects light on all light spectrum) of any shape (a cube for instance). If we plunge this object into darkness, we won't see anything: it does not emit light. If we light a red light, it takes the red colour. If we light a blue light, it becomes blue and so on. It is in fact a matter of reflection: the object sends back a light of the received colour.
Entities in game will be able altogether to reflect received Stimuli in the same way. Indeed each received Stimulus can influence the state of some entities and modify their Stimuli emission. However, we must pay attention to the fact that an Entity which receives blue light and yellow light will not send back two Stimuli of the two colours but only a green one. In fact each Stimulus has modified the Entity state and the Entity emits new Stimuli from this modified state.