the bird that fell into the gap due to a lapse of concentration.
left to rot - too pure to eat, not pure enough to bring close
(in the discussion about uses for impure terumah food, there is an argument between Reish Lakish and R. Yohanan if impurity is intrinsic or extrinsic. relevant to this is the case of a bird that due to lapse in concentration it is no longer suitable to sacrifice even though it is pure. The priest would throw the bird in the gap between the altar and the ramp to rot overnight before burning. so it can be intrinsically invalid. poor bird. not one thing or the other. fallen in the gap in-between definitions so left to rot.)