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1. A woman cannot become pregnant with another child when she is already pregnant.
2. Yehudah and Chizkiyah, the sons of Rebbi Chiya, were twins born three months apart.
3. One should always discuss the reason for a Halachah, even if he might be ridiculed (i.e., people will say that it is obvious).
4. The remains of a decomposed body that was laid to rest may or may not cause Tum'ah.
5. A person who was burned to death but whose body remained intact causes Tum'ah.
A BIT MORE
1. Twins must be the result of a single conception, although it is possible that they will leave the womb at very different times (see #2 below).
2. One was fully formed and left the womb in the beginning of the seventh month. The other took longer to form and left the womb only at the end of the ninth month.
3. This is to ensure that he knows the reason of the Halachah and will not think that it is due to some other reason.
4. If the body was laid to rest in a marble coffin or on a stone floor, its remains cause Tum'ah, since what is present is clearly from the remains of the corpse. If the body was laid to rest in clothes, in a wooden coffin, or on a brick floor, its remains do not cause Tum'ah, since it is very possibly the remains of the clothes or wood.
5. The Gemara relates an incident in which such a burned body was in a house, and the Chachamim ruled that the large openings in the house (of four Tefachim and more) were Tamei, and the small openings were Tahor.
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