Ibn Abbas (may Allah be pleased with them both), concerning "every animal with claws" [Surah al-An'am: 146], said: It means the camel and the ostrich. And concerning His words "except what their backs carry" [Surah al-An'am: 146], he said: It means the fat that clings to the back; and "or the entrails" [Surah al-An'am: 146] means the intestines (where the dung collects).
Ibn Abi Najih narrated the same meaning from Mujahid (may Allah have mercy on him), as his own words, in explaining "every animal with claws" and "the entrails".
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19703