In case, like me, you need a reminder of when to use "lay" and when to use "lie," go here. Which reminds me, here's yet another picky, anachronistic but useful entry from Fowler's Modern English Usage, Second Edition (1926):
Parthian shot. It seems to be a coincidence that the popular corruption parting shot, which no doubt owes its origin to the similarity of sound, has a meaning akin to that of the parent phrase. Parthian shot refers to the tactics of the Parthian mounted archers, who would discharge a volley into the enemy while moving smartly out of range of retaliation; parting shot is ordinarily used to describe a 'last word' fired by one of the parties to an argument at the other before breaking off the verbal engagement. Although the Parthian tactics were undoubtedly formidable, it is a MISAPPREHENSION to use Parthian shot to mean merely an attack that strikes home; the essence of it is that the attack is made at the moment of retreat.