Trick or treat!
I found this photo here.
Clipped from the Wikipedia entries onHalloween and Trick-or-treating:
Halloween has its origins in the ancient Celtic festival known as Samhain.[...] The term Halloween is shortened from All Hallows' Even.[...] The carved pumpkin, lit by a candle inside, is one of Halloween's most prominent symbols in America, and is commonly called a jack-o'-lantern. Originating in Europe, these lanterns were first carved from a turnip or rutabaga.
The practice of dressing up in costumes and begging door to door for treats on holidays goes back to the Middle Ages, and includes Christmas wassailing. Trick-or-treating resembles the late medieval practice of souling, when poor folk would go door to door on Hallowmas (November 1), receiving food in return for prayers for the dead on All Souls Day (November 2).
So, get out your Rutabagas! For some more photos of trick-or-treating ponies, visit this gallery courtesy of the ClickRyder email list.
Or if you are feline-fine, visit this gallery of costumed cats!