An onain, and one who clears away a pile of rubble, likewise one whom they have promised to release him from prison, and a sick or an aged person able to eat the volume of an olive, they slaughter on their behalf.  For any of these they may not slaughter for them alone, lest they cause the pesach-offering to become invalid. Therefore, if any disqualification befall them they are exempt from participating in the second pesach, except for the one who was clearing a pile of rubble, for he was [found to be] con- taminated retroactively.