R. Yossi says: Sometimes he is one and they slaughter it for him, and sometimes they are ten, and they do not slaughter it for him. How so? If he is one and he can eat it (i.e., the whole thing), they slaughter it for him. If they are ten and cannot eat it, they do not slaughter it for them, in order not to render the Pesach invalid (by remaining beyond its allotted time for complete consumption.)
R. Elazar b. Mattia says: Because we find that the congregation brings the Pesach in a state of tumah (uncleanliness) when the majority are unclean, I might think that one (individual) could tip the scales to tumah; it is, therefore, written "You may not sacrifice the Pesach offering by means of one."