I have heard that we can not earn any merit or demerit in any birth other than the human birth.
So my question is, do our sins (demerits) burn away in animal or tree birth?
E.g., a dog born in dirty mud has to face many difficulties to survive but a dog born in a bungalow may have all the comforts and facilities to lead a happy life.
Given that, do our merits and demerits really wipe off in an animal birth?