Hullin, Chapter One, Mishnah Six
1) [The method of killing] which renders the red cow valid renders the heifer invalid, and the method which renders the heifer valid renders the red cow invalid.
2) [The disability] which does not disqualify priests disqualifies Levites, and [the disability] which does not disqualify Levites disqualifies priests.
3) That which cannot be rendered unclean in earthenware vessels can be rendered unclean in all other vessels, and that which cannot be rendered unclean in all other vessels can be rendered unclean in earthenware vessels.
4) That which cannot be rendered unclean in wooden things can be rendered unclean in metal things, and that which cannot be rendered unclean in metal things can be rendered unclean in wooden things.
5) When bitter almonds are subject to tithing sweet almonds are exempt, and when sweet almonds are subject to tithing bitter almonds are exempt.
Section one: The red cow used in the purificatory process is slaughtered by shechitah, having its neck sliced, the same way all sacrificial animals are slaughtered (see Numbers 19:3). The heifer is the calf killed when a corpse is found and it is unknown who murdered the person. This heifer is killed by having its neck chopped from behind (see Deuteronomy 21:4). One cannot slaughter the red cow by chopping its neck from behind or the heifer by slicing it from the front.
Section two: Levites can serve in the Temple from the age of 20 to 50 (see Numbers 4:3). In contrast, priests can serve in the Temple from the time they reach majority age and they can continue as long as they want. In that sense, the age which disqualifies Levites does not disqualify priests.
Priests who have certain physical blemishes cannot serve in the Temple (we will learn about this more in the seventh chapter of Bechorot). These blemishes do not disqualify Levites.
Section three: When something impure enters the airspace of an earthenware vessel, it is rendered impure. However, if it touches the outside of the vessel, the vessel is pure. In contrast, other vessels are rendered impure when something impure touches them, either from inside or outside, and they are not impure when something enters their airspace without touching them.
Section four: A vessel that does not have a receptacle is considered simple in mishnaic terms. A simple wooden vessel cannot become impure, whereas a simple metal vessel can.
Unfinished metal vessels that can be used cannot become impure until they are completed. In contrast, an unfinished wood vessel can become impure as soon as it is usable.
Section five: Bitter almonds are edible when they are small and inedible when they become larger. Therefore they are liable for tithes when they are small and not when they are big.
Sweet almonds are opposite. When they are small they are inedible and therefore exempt from tithes. When they become larger and edible, they are liable for tithes.