Now consider these lines from Pound’s Canto LXXIV, which the OED cites in its entry on bull$hit as a verb:
Hey Snag wots in the bibl’?
Wot are the books ov the bible?
Name ‘em, don’t bull$hit ME.
This is a call for the facts. The person addressed is evidently regarded as having in some way claimed to know the Bible, or as having claimed to care about it. The speaker suspects that this is just empty talk and demands that the claim be supported with facts.
He will not accept a mere report; he insists upon seeing the thing itself. In other words, he is calling the bluff.
The connection between bull$hit and bluff is affirmed explicitly in the definition with which the lines by Pound are associated:
As v. trans. and intr., to talk nonsense (to);…also, to bluff one’s way through (something) by talking nonsense.
It does seem that bull$hitting involves a kind of a bluff. It is closer to bluffing, surely, than to telling a lie…
…just what is the relevant difference here between a bluff and a lie?
Lying and bluffing are both modes of misrepresentation or deception…
The liar is essentially someone who deliberately promulgates a falsehood.
Bluffing, too, is typically devoted to conveying something false. Unlike plain lying, however, it is more especially a matter not of falsity but of fakery.
This is what accounts for its nearness to bull$hit. For the essence of bull$hit is not that it is false but that it is phony…
…what is wrong with a counterfeit is not what it is like, but how it was made.
From: pages 44 – 47 of On Bull$hit by Harry G. Frankfurt