Interesting presentation. About the ox and ass, at ~12:30, he refers to the kosher regulations, Deuteronomy 14:4–8, and also to Deuteronomy 22:10 You shall not plow with an ox and an ass together. The symbolism is the uniting of clean and unclean, Jew and Gentile. (cf.Rom. 10:12. Gal. 3:28, Col. 3:11)
Earlier he says (~5:17): "By the way, the ass and the ox is one of the oldest elements of the nativity. It doesn't say in scripture that there's an ass and an ox specifically..."
It is true this is not explicit in the NT infancy narratives (Matthew and Luke) but it is specific in scripture:
Isaiah 1:3 The ox knows its owner, and the ass its master's crib (LXX: φάτνην, from φάτνη, manger); but Israel does not know, my people does not understand. (Cf. Lk. 2:7, 12, 16,φάτνῃ; from φάτνη, manger)
