Three little girls sit together in a room, playing with the toys surrounding them. One of the girls -- "Emma" -- has clearly taken charge of the group, and the others happily go along with her. A fourth girl -- "Jane" -- enters the room, hiding her face while clinging to her mother. The first three continue to play, while mom sits Jane down with some toys a few feet away from the group. After mom leaves, however, Jane sits alone against the wall. Emma makes her way over to Jane, inviting her to play with the rest of the group. Jane -- looking trapped -- starts to cry, then stands up and tries desperately to open the door.

Source: Inhibited children become anxious adults: Examining the causes and effects of early shyness