Dogs and Islam

Responding to this post, Aakar Patel writes in:

Dogs are thought unclean by Arabs not for western influence, but because of an utterance of the prophet, I think recorded by Sahih al-Bukhari. This continues from the Semitic tradition of labeling some animals unclean—shellfish and swine etc—and is no more remarkable than bestowing divinity on animals.

I agree with that last bit, but will not elaborate, lest cow worshippers attack me with 295(a).