Challah, Chapter 1, Mishnah 9. This mishnah lists the points that challah and Terumah have in common - the laws that apply equally to both.
The laws that apply equally to challah and Terumah:
"Chayavin aleha misah v'chomesh" - a non-kohen who ate challah or Terumah is liable to death at the hands of Heaven. And when he pays the kohen for what he ate, he must pay the principal plus a fifth - a fifth calculated from the outside, which comes to twenty-five percent, a fifth reckoned from the total after the additional payment is included.
"Va'asurin l'zarim" - a non-kohen is forbidden to eat them. At first glance this ruling seems unnecessary, since we have already been told that a non-kohen who eats them is liable to death and to payment of the principal plus a fifth. Some say that indeed it is not needed; and others explain it according to the view of Rabbi Yochanan in the Gemara in Niddah, that half a measure is forbidden by Torah law: the liability for death and for the added fifth applies only to one who eats a full measure, a kezayis, whereas one who eats even less than a kezayis has still transgressed a Torah prohibition. That is the novelty in the ruling "va'asurin l'zarim."
"V'hen nichsei kohen" - challah and Terumah are considered the kohen's own property, and he may use them to purchase whatever he wishes: slaves, land, and a non-kosher animal.
"V'olin b'echad u'me'ah" - both are nullified in one part out of a hundred. Even though a substance mixed with its own kind is generally nullified in one part out of sixty, Terumah and challah are nullified only in one part out of a hundred.
"Utz'richin netilas yadayim" - before eating challah and Terumah, and in practice even before merely touching them, one must wash his hands. We wash our hands only for eating bread, and even that is because we treat bread with the stringency of Terumah; but with Terumah itself the obligation to wash applies even to mere contact.
"V'ha'arev shemesh" - one who is tamei may not eat Terumah and challah, and even after he has immersed in a mikvah that is not enough; he must wait until the sun has set, darkness has fallen, and the stars have come out. Only once nightfall has arrived may he eat them - unlike ma'aser sheni, which may be eaten immediately after immersion.
Separating from the pure for the impure, and separating from what is adjacent:
One does not separate Terumah or challah from pure produce for impure produce. The separation must be done "min hamukaf" - that is, the produce from which one separates must be adjacent to the produce for which he is separating, and this law is derived from a verse. The reason one does not separate from the pure for the impure is a rabbinic decree: there is a concern that he will not place the pure produce next to the impure produce, lest it become tamei, and the result would be that he did not separate from what is adjacent. But the basis for all this is the very obligation to separate from what is adjacent, with the two placed near one another.
"Min hadavar hagamur" and a recognizable remainder:
Challah and Terumah may be separated only from produce whose processing has been completed, and not from produce whose processing has not yet been completed.
Similarly, one who says "my entire threshing floor is Terumah" or "my entire dough is challah" has said nothing, unless he leaves over a portion. For the essence of Terumah and challah is separation: a person takes from them the first part, the very first portion, and it cannot be considered a first portion when nothing is left over and everything has become Terumah or challah. Therefore it is required that "shirayah nikarin" - that its remainder be recognizable - and without this the separation is ineffective.
In summary: in this mishnah we listed the points that challah and Terumah have in common: the liability to death and to an added fifth for a non-kohen who eats them, their prohibition to a non-kohen even in less than the minimum measure, their status as the kohen's property, their nullification in one part out of a hundred, washing the hands, waiting for nightfall, separating from what is adjacent and not from the pure for the impure, separating from produce whose processing has been completed, and the need for a recognizable remainder.