Entity

An entity is anything in the Minecraft world which is not a block or other item that is placed in the cubical grid. Everything which can move around is an entity.

General behavior
Most entities have these properties:
 * A position, velocity, and rotation (as according to ordinary Newtonian physics).
 * A specific volume they occupy, which is a 3-dimensional box with a fixed height and width (square when viewed from the top, and not rotating).
 * Current health.
 * Whether they are on fire. Fire reduces health gradually and displays flames covering the entity.

Entities can be pushed around by water currents.

Types of entities
The following types of entity currently exist in Minecraft Beta. Entities listed as “solid” obstruct the passage of other entities; entities of all types cannot pass through solid blocks.

Further notes
Reverse engineering of the Minecraft network protocol suggests that paintings may be entities, but they are unusual in that they are aligned to the block grid and completely immobile. Doors and portals, the other objects larger than a single block, are actually groups of adjacent door/portal blocks.

Arrows, TNT, sand, and gravel are assumed to have infinite health because they are not destroyed by multiple TNT explosions (they can be fired out of cannons), nor by being on fire for long periods.

Boats and Minecarts
Boats and minecarts appear to recover health over time. For example, they can be broken by two arrows but only in quick succession, and minecarts never break as a result of being on fire (though they will break if they remain in contact with lava). (Boats are quickly destroyed by fire.) The amount of wobbling displayed by boats and minecarts when struck appears to indicate their current health.

Sand and gravel
The following description refers to sand for brevity, but gravel behaves in exactly the same way.

Sand normally exists as a block. When a sand block's support is removed, it turns into a sand entity and falls down until it hits another object, at which point it places itself as a block in the nearest on-grid position, or turns into a dropped sand item if that position is occupied (such as by a torch). While sand ordinarily falls straight down, it can be redirected while falling by explosions.

If there is a boat or minecart in the way of falling sand, it will place itself as a block above the vehicle, but then immediately fall down again, producing a 'hopping' effect. This can be used in the construction of a sand cannon.

If when the world is created, a cave is generated underneath sand, then the sand will not notice that it should fall down and will remain floating until a block is removed from under it, or beside it. This latter fact means that a single falling sand block can trigger the entire region of sand to fall down; therefore, sand ceilings should not be disturbed unless one is outside the area, standing over a torch, or prepared to dig out quickly once the sand has fallen.