Our Mishna says onen is exempt from mitzvos when the dead body is in front of him, but the Braisa seems to contradict this. The Braisa says it is preferable not to eat in front of a dead body unless there is no other option and one could then just turn their face the other way and eat. The Braisa then continues to say an onen is exempt from mitzvos, clearly implying whether or not they are in the presence of the dead body! The Gemara gives 2 answers- either the exemption is only when one is in presence of the body and the Braisa only exempted the onen in that case, or alternatively, the exemption is even when not in the presence of the body, and our mishna uses "the body is front of him" loosely and it really means any time the body is not yet buried.

Another exemption from mitzvos is for someone watching the dead body, bc they too are engaged in a mitzvah.

Within 4 amos of a dead body one should not perform a mitzvah bc it mocks the dead

There is a dispute if a dead body needs to be watched on a boat where it is unlikely there are mice

One should not transport bones on a dead person or a Sefer Torah while riding astride them.

It is a big mitzvah to escort a dead body and wrong to see the body being escorted and not join in

R Chiya and R yonasan dispute whether the dead are aware of what happens here. For example, having tzitzis drag on a grave. The Gemara later clarifies they def are aware of pain to their own bodies.

There is a concept that the righteous living are called alive after death and the wicked are called dead even when alive.

Benayahu increased Torah, was the greatest in times of the Temples, broke through ice to dip in a mikvah, and finished Sifra in one day

There is a concept of the dead finding out about things in this world from those who pass away or from certain declerations made in Heaven.