Now, if the external reality is not changing anymore, there could be a problem: the model has to make a new prediction, but there is no reason to do this. Such a situation can also produce a temporary perturbation of the stability of the structure of models, i.e. irritation. In such a situation, the brain could activate other ZMs, (e.g. ZMs which are not connected to the unchanging external reality) up to the moment when there will be a change in the main external reality. This activity could be a source of mistakes or even accidents, as the local-ZM becomes, temporarily, one, which is not connected to the main external reality. The accidents can occur, for instance, when the external reality is changing and the suitable local-ZM has not enough time to reinitialize. Example: a driver is in a hurry and stops at a stoplight. The external reality is not changing for a while and so there could be an irritation. Under stress conditions, the driver could activate another model (associated or not to the external reality) and so, he/she is not properly prepared for the moment when the traffic light changes to green. Because this is an important source of irritation, in some cities there is an additional display, which counts the time for red or green status, and so the irritation is diminished. Thus, time flows with a variable speed, depending on the speed of change of the external reality (see ETA about "time"). 11c. The word "irritation" is used also when an external factor interferes with the activity of a main model. This external factor could also activate the PSM. Such a situation can also affect the stability of the structure of models and so, produce irritation. As we know, faced with a new external reality (for instance a strong noise), the brain will switch from the actual-ZM to another model, which understands the new situation. When such external perturbation occurs on and on, the brain is forced to switch the ZMs very often. Such activity can be affected by mistakes, because switching from a model to another is a very complex activity. When a model is deactivated, some information has to be stored to be used when the model will be reactivated. Sometimes, the external reality can change so much that the stored information becomes of no use. But the brain does not know easily if the stored information is good or not at the new activation. So, there could be mistakes, and the stability of the structure of models can also be affected (irritation occurs). Because the activation and deactivation of a symbolic model is much more complicated than for an image model, the switching between a symbolic model and an image model, or even worse, between two symbolic models, is very dangerous (don't use the mobile phone when you drive, e.g.) 12. Love, to love