An onain immerses [himself] and eats his pesach-offering in the evening, but [may] not [eat other] offerings.  One who hears about the death of his relative, or one who has arranged for bones [of a close relative] to be gathered on his behalf, immerses [himself] and eats of offerings.  [If] a proselyte had been converted on the eve of Pesach —- Beis Shammai say he immerses [himself] and eats of his pesach-offering in the evening.  But Beis Hillel say: One who separates [himself] from an uncircumcised state is like one who separates himself from the grave.

One who was contaminated or was on a distant journey, and had not observed the First [Pesach], must observe the Second. [If] he erred or was prevented, and [therefore] did not observe the First [Pesach], he must observe the Second. If so, why is it said: One who was contaminated or was on a distant journey (Numbers 9:10)? Because these are exempt from kares, but those are liable to kares.