Vaishnava Dharmashastra 23.49

23.49

nityam āsyaṃ śuci strīṇāṃ śakuniḥ phalapātane
prasrave ca śucir vatsaḥ śvā mṛgagrahaṇe śuciḥ //

The mouth of a woman is always pure (for the purpose of a kiss); a bird is pure on the fall of fruit (which he has pecked); a sucking calf (or child), on the flowing of the milk; a dog, on his catching the deer.