1) Ch. 9, v. 3: "S'ir izim l'chatos" A goat as an atonement offering Since this is brought to atone for their part in the sin of the golden calf, why weren't they commanded to bring a calf, just as Aharon was?
2) Ch. 9, v. 8: "Va'yikrav Aharon el hamizbei'ach" And Aharon approached the altar After much hesitation Aharon was convinced by Moshe to do the priestly service. At this point in time both Moshe and Aharon officiated as Kohanim G'dolim. The gemara Megiloh 9b relates that one time the Kohein Godol became temporary disqualified from doing the service and Rabbi Yoseif ben Ulom of Tzipori was elevated to the position of Kohein Godol in the interim. When the regular Kohein Godol was again qualified to serve, Rabbi Yoseif was left in limbo. He could now not serve as a regular Kohein, as once he was elevated he could not be demoted. As well, he could not continue being a Kohein Godol concurrently with the regular one because having two people in this position would cause animosity. He was no longer able to do service as a Kohein. How then, were Moshe and Aharon Kohanim G'dolim concurrently?
3) Ch. 10, v. 2: "Va'teitzei aish milifnei Hashem vatochal osom" And a fire went out from in front of Hashem and consumed them It is most unusual to find the name Hashem used here, where a most devastating punishment was meted out to Nodov and Avihu, since Hashem connotes the characteristic of mercy.
4) Ch. 10, v. 2: "Va'yomusu lifnei Hashem" And they died in front of Hashem The Holy Zohar writes that Nodov and Avihu were under the age of 20 years when they committed their sin. This raises the question of how they were punished by Heaven, based on the ruling that the Celestial court does not punish someone who is under the age of 20.
5) Ch. 10, v. 19: "Vatikrenoh osi ko'eileh v'ochalti chatos ha'yom" And if it has happened to me like this and I were to eat the atonement offering today Rashi says that Aharon told Moshe that although a mourner has the leniency to partake of the offering that was unique to the inauguration of the Mishkon, the same does not apply to the Rosh Chodesh atonement, which was a sacrifice for all time. How did Aharon know this difference?