The food that is caten by a person from which a part has already been extent by another, or which is eaten without a part thereof having been offered to gods and guests and children, is appropriated by Rakshasas. Such impure food, if offered to the deities and Pitris is never accepted by them but is appropriated by Rakshasas.
परोच्छिष्टं च यद् भुक्तं परिभुक्तं च यद् भवेत्। दैवे पित्र्ये च सततं तं भागं रक्षसां विदुः॥