Musar su Levitico 19:8

Rabbi Menachem Habavli has this to say when dealing with the reason of the negative commandments in this portion: The reason that the נותר must not be eaten, (the time-limit for consumption of the sacrificial meat, about which the Torah writes in 19,18 that if someone were to ignore this time-limit he would bear his guilt) is that the sin brought about by such eating becomes an accuser against the transgressor along with the angel appointed for this very sacrifice on that very day. The angel whose "meal" has thus been cursed will look upon such a person with ill favor. This becomes even more serious if someone else for whom this meat had never been intended were to eat it now that it carries a curse. This is why the Torah goes into details saying: ואכליו עונו ישא, anyone eating of this left-over will carry his guilt, i.e. the sin of the person consuming it will rest on the shoulders of the person who had originally owned the sacrifice and had neither eaten it up nor burned its remains.