(Devarim 19:5) "and his hand swing the axe": From here it is ruled that if he intended to chop down a tree and it fell on a man and killed him, he is exiled.
"and it find his neighbor and he die": to exclude his presenting himself. From here R. Eliezer b. Yaakov ruled: If, after the stone left his hand, the other put out his head and was hit by it, the first is not liable.
וְנִדְּחָה יָדוֹ בַגַּרְזֶן לִכְרוֹת הָעֵץ, מִכָּן אַתָּה אוֹמֵר: נִתְכַּוֵּן לָקוּץ אֶת הָאִילָן וְנָפַל עַל אָדָם וַהֲרָגוֹ – הֲרֵי זֶה גּוֹלֶה.
(Devarim 19:5) "and his hand swing the axe": From here it is ruled that if he intended to chop down a tree and it fell on a man and killed him, he is exiled.
וְנָשַׁל הַבַּרְזֶל מִן הָעֵץ הַמְבַקֵּעַ, רַבִּי אוֹמֵר: מִן הָעֵץ הַמִּתְבַּקֵּעַ.
"and the blade slip from the wood": from the haft (of the axe). Rebbi says: from the wood that was being chopped.
וּמָצָא, בַּמָּצוּי. מִכָּן הָיָה רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב אוֹמֵר: אִם מִשֶּׁיָּצָאת אֶבֶן מִיָּדוֹ הוֹצִיא הַלָּה אֶת רֹאשׁוֹ וְקִבְּלָהּ – הֲרֵי זֶה פָּטוּר.
"and it find his neighbor and he die": to exclude his presenting himself. From here R. Eliezer b. Yaakov ruled: If, after the stone left his hand, the other put out his head and was hit by it, the first is not liable.
הוּא יָנוּס אֶל אַחַת הֶעָרִים הָאֵלֶּה וָחָי, שֶׁלֹּא יְהֵא גּוֹלֶה מֵעִיר לְעִיר.
"he shall flee to one of these cities": He may not exile himself from one city to another.
(דברים יט ו) פֶּן יִרְדֹּף גֹּאֵל הַדָּם אַחֲרֵי הָרוֹצֵחַ, מִצְוָה בְּיַד גּוֹאֵל הַדָּם לִרְדֹּף.
(Ibid. 6) "Lest the redeemer of blood pursue the slayer": It is a mitzvah for him to pursue him.
כִּי יֵחַם לְבָבוֹ וְהוּא לֹא שֹׂנֵא הוּא לוֹ, הָא אִם שׂוֹנֵא – אֵינוֹ גוֹלֶה.
"not having hated him": If he had hated him, he is not exiled.
מִתְּמוֹל שִׁלְשׁוֹם, זוֹ שֶׁרַבִּי יְהוּדָה אוֹמֵר: תְּמוֹל – שְׁנַיִם; שִׁלְשׁוֹם – שְׁלֹשָׁה.
"mitmol shilshom": As R. Yehudah says: "tmol": two days; "shilshom": three days (see #181).
(דברים יט ז) עַל כֵּן אָנֹכִי מְצַוְּךָ לֵאמֹר – לְהַזְהִיר בֵּית דִּין עַל כָּךְ.
(Ibid. 7) "Therefore, I command you, saying": Beth-din is being exhorted to this end.