Pumpkin

A Pumpkin is a type of block which was introduced in the Halloween update. They appear on grass in a similar manner to that of mushrooms. They can appear alone or in groups. It is rumored that dungeons may appear more commonly below a pumpkin patch, however there is absolutely no evidence to support this claim.

Currently, you can only find them with a carved face. Originally it was stated by Notch that they were to be found and then subsequently carved by crafting.

Harvested pumpkin can be equipped as a helmet without any actual armor value; it is, however, unique due to it limiting the player's view of the world as seen from inside the pumpkin. The pumpkin helmet can be removed and placed into inventory.

Pumpkins cannot be placed without a block under them. However, you can place it, then remove the block directly under it and it will stay in place. This reveals that the bottom texture is the same as the top. When placed, pumpkins automatically face the player the best they can.