During examination of a severed finger, Ducky says, "The Romans believed that one should wear the wedding ring on the fourth finger of the left hand...yes, because a vein in that finger runs straight through to the heart. Vena amoris." As romantic as this traditional belief is, in this case it's proved wrong since all the fingers in the hand have a similar vein structure.
Abby makes a reference to Mercury being in retrograde. In astrology, Mercury rules communication, clear thinking, truth and travel. So when the planet goes retrograde, which means that it looks like it's moving backwards in the sky, all those things also move backwards. Things start to get ugly as they tangle up.