1. The Gemara discusses the type of bone of the Korban Pesach which one may not break.
2. The Rabanan decreed that contact with Pigul or Nosar causes one's hands to become Tamei.
3. It is clear that there never was a decree that the meat of a Korban Pesach should become Tamei if taken from one group to another.
4. It is forbidden to take a Korban Pesach from one group to another group, even if both groups are eating in the same house.
5. This prohibition (#4) is transgressed only if there is an act of Akirah from its original place and an act of Hanachah in its new place, similar to the liability for transferring from one type of domain to another on Shabbos.
A BIT MORE
1. It is a bone that has a k'Zayis of flesh either on the outside or the inside (marrow) of the bone.
2. The Rabanan decreed Tum'ah on Pigul in order to prevent a Kohen from intentionally rendering his enemy's Korban Pigul. He will refrain from doing in order to prevent his hands from becoming Tamei. Similarly, they decreed Tum'ah on Nosar so that the Kohanim would not delay their consumption of the meat of Korbanos.
3. The Gemara explains that because the people would be careful with the Korban Pesach, there was no need to decree that it become Tamei if taken away from the immediate area of the group eating it, as this generally would never happen.
4. This is derived from the additional word "outside" in the verse which discusses the house in which the Korban is eaten. This word refers to outside the group that is eating it in the house, and forbids bringing it to even another group in the house.
5. This is because the term "taking out" is used with regard to carrying on Shabbos and with regard to carrying away the Korban Pesach to another group. We therefore derive that just as one is liable on Shabbos only if he performs an Akirah and a Hanachah, he is liable for bringing the Korban Pesach to another group only if he performs an Akirah and a Hanachah.