(Exodus 21:33-34) "If a man opens a pit." Rabbi Elazar said: Two things are not within a person's possession, yet Scripture treated them as though they were within his possession, and these are they: a pit in the public domain, and leavened bread from the sixth hour onward. Rabbi Elazar said, and some report it was taught in a baraita: Four things the Torah reduced concerning their safeguarding, and these are they: pit and fire, tooth and foot. Pit, as it is written, "if a man opens a pit and does not cover it" - thus if he covered it he is exempt. Fire, as it is written (Exodus 22:5), "the one who kindled shall surely make restitution" - he is liable only when he acts in the manner of one who kindles. Tooth, as it is written, "and it consumed" - he is liable only when it acts in the manner of consuming. Foot, as it is written (there), "and let loose" - he is liable only when it acts in the manner of letting loose.
Pit and Fire, Tooth and Foot, and the Limits the Torah Set
Yalkut Shimoni on Torah 341:8
(שמות כא לג-לד) כִּי יִפְתַּח אִישׁ בּוֹר, אָמַר רַבִּי אֶלְעָזָר, שְׁנֵי דְּבָרִים אֵינָן בִּרְשׁוּתוֹ שֶׁל אָדָם וַעֲשָׂאָן הַכָּתוּב כְּאִלּוּ הֵן בִּרְשׁוּתוֹ, וְאֵלּוּ הֵן, בּוֹר בִּרְשׁוּת הָרַבִּים, וְחָמֵץ מִשֵּׁשׁ שָׁעוֹת וּלְמַעְלָה. אָמַר רַבִּי אֶלְעָזָר, וְאָמְרֵי לָהּ בְּמַתְנִיתָא תָּנָא, אַרְבָּעָה דְּבָרִים מִעֲטָה תּוֹרָה בִּשְׁמִירָתָן, וְאֵלּוּ הֵן, בּוֹר וָאֵשׁ, שֵׁן וָרֶגֶל. בּוֹר, דִּכְתִיב כִּי יִפְתַּח אִישׁ בּוֹר וְלֹא יְכַסֶּנּוּ, הָא כִּסָּהוּ פָּטוּר. אֵשׁ, דִּכְתִיב (שמות כב, ה) "שַׁלֵּם יְשַׁלֵּם הַמַּבְעִר", עַד דְּעָבִיד כְּעֵין הַמַּבְעִיר. שֵׁן, דִּכְתִיב "וּבִעֵר", עַד דְּעָבִיד כְּעֵין וּבִעֵר. רֶגֶל, דִּכְתִיב (שם) "וְשִׁלַּח", עַד דְּעָבִיד כְּעֵין וְשִׁלַּח.