(Rav Mesharshiya): Rav Acha bar Rav exempted due to a verse:

"Mos Yumas ha'Makeh Rotze'ach Hu" - a murderer is liable for Metzamtzem, but a damager is not.

(Rava): If Reuven tied up Shimon and Shimon starved to death, Reuven is exempt. (The cause of death, i.e. hunger, came by itself.)

(Rava): If Reuven tied up Shimon in a hot sun or in the cold and he died from this, Reuven is liable;

If he tied him up before the sun shone there or before it was cold, but knowing that the sun or cold will later come, he is exempt. (This is only Grama, i.e. causation.)

(Rava): If Reuven tied up Shimon in front of a lion, he is exempt (Rashi - Shimon could not have escaped even if he was not tied up; Tosfos - since Reuven had time to tie him up, surely the lion was not yet upon him);

If he tied him up in front of a swarm of mosquitoes and they killed him, he is liable.

(Rav Ashi): Even if he tied him up in front of mosquitoes, he is exempt. (Perhaps) the ones chasing him went away, and others came and killed him.

(Rava or R. Zeira): If Reuven tied a barrel over Shimon (and he suffocated) or he uncovered the roof over him (allowing the cold in, which killed him) he is liable;

(The other of Rava and R. Zeira): He is exempt.

Inference: Rava must exempt, for Rava taught that if he tied him up and he starved to death, he is exempt.

Objection: R. Zeira must exempt, for he taught that if Levi locked Yehudah in a marble house and lit a fire (and the heat killed him), he is liable;

Inference: Had he not lit the fire, he would be exempt!

Answer: There, had he not lit the fire, he would be exempt because the cause of death (the heat) did not begin yet.

When he tied a barrel over him, the (lack of air, the analog of the) heat is there from the beginning.

(Rava): If Reuven pushed Shimon into a pit with a ladder, and Yehudah or even Reuven himself removed the ladder (leaving Shimon to die), he is exempt, because when he pushed him in, it was possible to leave. (Removing the ladder is only Grama.)

(Rava): If Shimon was holding a shield, and Reuven shot an arrow at him, and Yehudah or even Reuven himself removed the shield, he is exempt;

This is because his liability the arrow ended at the time he shot it (it was not prone to kill. Removing the shield is only Grama.)

(Rava): If Shimon was holding medicine (that could heal him from being hit with an arrow), and Reuven shot an arrow at him, and Yehudah or even Reuven himself removed the medicine, he is exempt;

This is because when he shot the arrow, Shimon could have cured himself.

(Rav Ashi): Therefore, even if Shimon was not holding medicine but he could buy it in the market, Reuven is exempt.

Question (Rav Acha brei d'Rava): If when Reuven shot the arrow Shimon did not have a way to obtain medicine, and later Shimon had an opportunity but did not cure himself, what is the law?

Answer (Rav Ashi): Once Shimon had an opportunity to cure himself, Reuven is permanently exempted.

(Rava): If Reuven threw a rock at a wall and it bounced back and killed, he is liable.

Support (Beraisa): If Levi was playing with a ball (to bounce it off a wall), and it bounced back and killed someone:

If Levi was Mezid, he is killed;

If he was Shogeg, he is exiled (he must stay in an Ir Miklat).

Objection: This law (Galus) is obvious!

Answer: The Chidush is the first law, that if he was Mezid, he is killed;

One might have thought that since it is not clear that it will bounce back, the warning is doubtful and he is exempt. The Beraisa teaches that this is not so.

(Rav Tachlifa bar Ma'arava - Beraisa): If Levi was playing with a ball (like above) and it bounced and killed someone within four Amos (of the wall), he is exempt (from Galus; some explain, from Misas Beis Din). Outside of four Amos, he is liable.

Question (Ravina): What is the case?

If he wanted it to go that far, he should be liable even within four Amos;

If he did not want it to go that far, he should be exempt even outside four Amos!

Answer (Rav Ashi): People who play with balls want the ball to bounce back as far as possible. (We assume that he did not want it to go less than four Amos.)

Inference: (Since he is liable, this shows that) bouncing a ball off a wall is considered one's Ko'ach (impetus).

Contradiction (Mishnah): If Reuven wanted to be Mekadesh (put ashes of the Parah Adumah on) water, and the ashes fell on his hand or on the side of the Keli holding the water and from there to the water, the Kidush is invalid.

Answer: The case is, the ashes came to rest, and then fell (by themselves, and not because he initially dropped them).

Question (Mishnah): If a needle was on earthenware, and one sprinkled Mei Chatas, and he is unsure if it went directly on the needle or if it fell on the earthenware and from there Mitzah (spurted) to the needle, the sprinkling is invalid.

Answer (Rav Chinena bar Yehudah): The text should say 'Matza' (it was found) on the needle (the earthenware is inclined. Perhaps it flowed down not due to human Ko'ach.)

(Rav Papa): If Reuven tied up Shimon and directed water to onto him, and it killed him, Reuven is liable for murder, for his action killed him. It is as if he shot an arrow at him;

This is only if he was right by Shimon when he directed the water. If not, he only caused the death, so he is exempt.

(Rav Papa): If Reuven threw a rock up and it came down and killed someone to the side, he is liable. (It killed due to Reuven's Ko'ach, not just due to gravity).

Question (Mar bar Rav Ashi): If it moved due to his Ko'ach, it should have continued in the direction he threw it, i.e. up!

Counter-question (Rav Papa): If it is not his Ko'ach, it should have gone straight down!

Answer (Rav Papa): Rather, the sideways movement is a weak component of Reuven's Ko'ach.