Shmirah: by Rabbi Stuart Kelman and

(10) Then Rizpah daughter of Aiah took sackcloth and spread it on a rock for herself, and she stayed there from the beginning of the harvest until rain from the sky fell on the bodies; she did not let the birds of the sky settle on them by day or the wild beasts [approach] by night.

The Gemara explains: As long as a person is alive [ḥai], he is feared by the animals. Once he dies, he is no longer feared.

From the mishna one can infer that when his deceased relative is laid out before him, yes, he is exempt from mitzvot. But, if it is not his relative and he is only watching over the deceased, no, he is not exempt. The Gemara challenges: Wasn’t it taught in a baraita: One who watches over the deceased, even if it is not his deceased relative, is exempt from the recitation of Shema, from prayer and from phylacteries, and from all mitzvot mentioned in the Torah? The Gemara responds that these two sources should not be understood as contradictory, but as complementary. In both the cases, he is exempt; where one watches over the deceased, but it is not his deceased relative, as well as the case where it is his deceased relative, but he is not watching over the deceased. The Gemara further challenges: We concluded that, in both cases, if it is his deceased relative or if he was watching over the unrelated deceased, he is exempt from mitzvot....

The baraita continues: If two individuals were watching over the deceased, this one watches and that one recites Shema, and then that one watches and this one recites Shema. Ben Azzai says: If they were traveling with the deceased on a boat, they are permitted to set the deceased down in this corner of the boat and both pray in another corner of the boat. The Gemara asks: What is the practical difference between these two opinions? Ravina said: The practical difference between them is whether or not one need be concerned about mice even inside the boat. The first Sage holds that we are concerned about mice everywhere, and it is therefore inappropriate to leave the deceased unguarded, even on a boat, lest he be eaten by mice. The other Sage, ben Azzai, maintains that we are not concerned about mice on a boat.

(3) He who has been bereaved of a relative for whom he has to keep the period of mourning is exempted from reading the Shema till he has buried the body, as his mind is not free for reading it. A watcher, even if the body is not that of a relative, is exempt from reading the Shema. When there are two watchers, one watches while the other withdraws to another room and reads it. Then he returns and watches while his companion withdraws and reads it....

All those [near-of-kin] for whom he²⁸The Kohen. defiles himself [applies] even [to a defilement] which is not for the requirements [of the corpse].²⁹

Gloss: And according to the former opinion, even if he²⁸The Kohen. suffered a bereavement on the Sabbath where it is impossible to bury him the same day [on account of the Sabbath], he²⁸The Kohen. is permitted to defile himself for him and guard him so that he should not lie in disgrace.³¹ (Ter. ha-Deshen s. 283) It is proper to adopt the stringent view according to the latter opinion [viz.,] that he²⁸The Kohen. should defile himself only for the requirements of the burial³² and [in order] to bring him a coffin and shrouds.³³

(9) One who collects bones [for final burial] and one who guards the corpse and the one who carries them from place to place is exempt from the reading of the Shema⁸ from Tefillah,⁸ from Tefillin⁸ and from all religious duties enjoined in the Torah, both during a weekday as well as during the Sabbath,³¹This applies on the Sabbath only to guarding the corpse or the bones, for no collection of bones is made on the Sabbath. and there is no difference whether [these are] the bones of near-of-kin or of strangers, both if he is in a boat or on the road, even if the collectors [of the bones] are many.³²This refers to those who collect the bones, but if there are many who guard the corpse or the bones, one guards and the other reads the Shema.

(10) The person who guards the deceased,⁷The deceased must be guarded from rodents. See Mishnah Beruch 71:12. even if he is not a mourner, is exempt from Kerias Shema and Shemoneh Esrei, and from all other mitzvos of the Torah,⁸ for he who is engaged in the performance of a mitzvah is exempt from performing another mitzvah.⁹ If there are two two watchmen, [they should alternate] one of them should guard, while the other says Krias Shema and Shemoneh Esrei.

(11) It is forbidden to eat [a meal] in the room where the deceased lies,¹⁰It is also forbidden to smoke in that room. (Sdei Chemed, Laws of mourning, 116.) unless there is a partition. It is even forbidden to have a snack, even to eat fruit or drink water is forbidden. It is necessary to instruct the guards about this. It is also forbidden to recite a berachah there.

One is exempt from saying the Shema and the Shmonah Esrei and other mitzvot because he is engaged in the mitzvah of guarding from rodents. Even on a ship we are concerned about rodents.