The corpse or severed limb of an animal make a person who moves or touches it or a utensil that touches it impure, as it says "[One who touches their corpses shall be impure until evening...] and one who carries their corpses shall wash his clothes and be impure until evening"¹; but if a permissible animal was properly slaughtered its corpse is not a source of impurity. The corpse of a permissible bird makes a person who eats it impure, as it says "And any person who eats a corpse... shall wash his clothes and bathe in water [and be impure until evening and become pure]".² The corpses or limbs of certain rodents and lizards make a person or utensil that touches them impure [as it says "This shall be impure for you of the things that crawl on the ground... anyone who touches them when they are dead shall be impure until evening; and anything that part of them falls on... shall be put into water and be impure until evening and become pure"³].^a

Semen is also a source of impurity by touch; and a man who has had a seminal emission or a woman who has had sexual relations are impure [as it says "And if semen comes out of a man he shall bathe all his flesh in water and be impure until evening; and any garment or skin that has semen on it shall be washed in water and be impure until evening; and if a man lies with a woman seminally they shall wash in water and be impure until evening"⁴]. Rabbinically, idols (by touch) and their offerings (by movement as well) are also sources of impurity, as it says "Remove the strange gods from your midst and make yourselves pure and change your clothes",⁵ and it says "[The idols of their gods you shall burn in the fire...] you shall abominate them",⁶ and it says "And they joined Baal Peor and they ate sacrifices to the dead".^7,b

Anything that makes a person impure when he moves it also makes things that he touches while moving it (or, except for an animal corpse and a saddle used by a person who makes seats impure: while touching it) impure. Otherwise, a person or thing that has become impure through contact with a source of impurity cannot -- except in the cases where he or it too becomes a source of impurity, as specified earlier -- make persons or utensils impure but can only make food and drink impure. Rabbinically they also make a person's hands impure, as do writings from the Bible (to ensure that they are not handled casually). If a person eats or drinks something impure or washes in "drawn water", or has bathed on account of impurity but the sun has not yet set, he too has this minor degree of impurity (which is that of food that has touched something that has touched a source of impurity); writings from the Bible must also be treated as though they had this degree of impurity.^c

Sources:
1. Lev. 11:24-28, 39-40	a. 1:1-2; 2:3; 3:1; 4:2,5
2. Lev. 17:15	b. 5:1,9; 6:1-2,7
3. Lev. 11:29-32	c. 6:12; 8:1-2,10; 9:1,5; 10:1; see 11:10-12; Tumas Mes 5:2,7; Parah Adumah 5:2; Metamei Mishkav u-Moshav 6:2
4. Lev. 15:16-18
5. Gen. 35:2
6. Deut. 7:25-26
7. Psalms 106:28