Midrash su Levitico 11:31

1) (Vayikra 11:32) "And all (vessels) upon which there falls of them (sheratzim) in their death shall be tamei." Of what is this verse speaking? If of their death, this has already been stated (Vayikra 11:31). If of ever min hameth (a limb of a dead animal), this is stated below (Vayikra 11:35). It must be speaking, then, of ever min hechai (a limb of a living animal, [and "in their death" signifies the death of the limb]). (But why is a verse needed for this?) Is it not derivable a fortiori? viz.: If a beast, whose blood was not equated with its flesh (to confer tumah), ever min hechai of it confers tumah, then a sheretz, whose blood was equated with its flesh, how much more so should ever min hechai of it confer tumah! (Why, then, is the verse needed?) No, if this is so with a beast, it may be so because it confers tumah by being carried. Would you, then, say the same for a sheretz, which does not confer tumah by being carried, (but only by being touched)? Since it does not confer tumah by being carried, (I would say that) ever min hechai of it does not confer tumah. It must, therefore, be written "And all (vessels) upon which there falls of them (sheratzim) in their death shall be tamei" — to include ever min hechai.

1) (Vayikra 11:29-31): "And this to you is what is unclean among the creeping things (sheratzim) which creep upon the earth: the weasel and the mouse, and the great lizard after its kind. And the gecko, and the land-crocodile, and the lizard, and the sand lizard, and the chameleon. These are what are unclean to you among all that creep." What is the intent of this? Because it is written (Vayikra 11:43): "Do not make yourselves tamei by them (sheratzim) and you will become tamei through them," I might think that inner-body tumah and the tumah of offerings are being spoken of; it is, therefore, written "And this (i.e., only this to you is what is unclean … the weasel and the mouse, and the great lizard, after its kind, etc." I might think that these confer tumah on men and implements and the others confer tumah on men but not on implements, or on implements but not on men; it is, therefore written (Vayikra 11:31): "These (are what are unclean to you"). Only these (confer tumah). Or, perhaps only these are excluded which are like the particular (kinds mentioned here, viz.:) Just as the particular have bones and reproduce, so, only those are excluded which have bones and reproduce. Whence do we derive (that also excluded are) those which have bones and do not reproduce or those which do not have bones and reproduce? From "These" are tamei to you among all that creep" — Only these among the sheratzim confer tumah.

1) (Vayikra 11:31): "These are what are tamei to you among all that creep": "what are tamei" (rather than just "tamei"): to include their skins (as well as their flesh). I might think (that this refers to) the skins of all of them. It is, therefore, written "These are (the skins of) what are tamei" — the skins of (Vayikra 11:30) the gecko, the land-crocodile, the lizard, and the sand-lizard. R. Yehudah says: The lizard is like the weasel (Vayikra 11:29). R. Yochanan b. Nuria says: Eight sheratzim have skins.