Because is Halloween :S , a Traditional night that children and young people celebrated since XIX century.
This people decorated their houses and streets with a typical Halloween symbols, for example: witches, black cats, pumpkins, candles, masks, parties and pranks, etc.
Halloween appeared in the U.S. during the late 1800's.
In 1848, millions of Irish emigrants poured into America as a result of the potato famine. With this sudden influx of people, the holiday of Druidism found its new home on alien shores.
-Halloween symbols:
Pumpkins have been an essential part of Halloween celebrations ever since, they were cut with faces representing demons and was originally intended to frighten away evil spirits. It was said that if a demon or such were to encounter something as fiendish looking as themselves that they'd run away in terror.
Black cats were considered to be reincarnated beings with the ability to divine the future, and also, the people believed that these creatures could communicate with the spirits of the dead.
To witches, Halloween is a festival of the dead, and represents the "end and the beginning of the witches year. At this time is considered the best time to contact spirits.
Well, to have a horrific Halloween :)