Matching the Opener to the Digger and the Common Thread Between Them

Another interpretation: it compared the one who opens to the one who digs, and the one who digs to the one who opens. Just as the one who opens is exempt when he has permission, so too the one who digs is exempt when he has permission; and just as the one who digs is liable only at the requisite depth, so too the one who opens is liable only at the requisite depth. Rabbi Yehudah ben Beteira says: the case of the one who opens is not like the case of the one who digs, and the case of the one who digs is not like the case of the one who opens. The feature common to both is: whatever a person is obligated to safeguard, he is liable for its damage; so too anything a person is obligated to safeguard, he is liable for its damage. I have only one who opens and one who digs; from where do I include one who plasters it or shapes it? The verse teaches, "and does not cover it" - thus it was not the opening or the digging that caused it, but rather the failure to cover. "And does not cover it" comes to include an unpaid custodian.