פירוש על עבודה זרה 147:4

R. Hiyya b. Abba clarifies that to be on the list in the mishnah, the substance needs to be something customarily sold by number, therefore it does not included hametz, which is sold by weight or volume. It also needs to be something which may not be put to any use, and therefore the list does not include meat not properly slaughtered, which may be used and just not eaten. However, the halakhah in the mishnah is true with regard to these substances, even though they are not listed.