Billy McGuinty's Ghost

[Achebe]

and that was the night Virgin Mary wept blood.

that's the punchline, but i failed to get it.
there's the allusion to virgin mary statues weeping blood, but the only connection i can think of between that an a pub, is a pun on 'bloody mary'. however, that makes sense only if the pub were serving virgin marys earlier...which they would never have done.