that we are one people with the lip down at 25 laeoklin a strong foul smell, until he was 18, and he asked the class, however, the smell of his body remained in the lip and lip comes to the floor there are 17 people.And they have this smell, which, of course, who added he surely thought it was smell the reek of someone down, that is; So the stink is the external impact is not caused by us, but we are all affected, there are two categories of external effects external positive (Positive Externalities), and the negative impact of external (Negative Externalities).