A tap is formed by a single contraction of the muscles such that one articulator is thrown against the other. (...) A flap is an articulation which usually involves the curling of the tip of the tongue up and back and then allowing it to hit the roof of the mouth as it returns to a position behind the lower teeth. A flap is therefore distinguished from a tap by having one articulator strike against another in passing while on its way back to its rest position, as opposed to striking immediately after leaving its rest position.