Hey, DOCTOR WHO continuity freaks and nitpickers (and you know who you are)!
Here's the thing: How could Strax the Sontaran be in "The Snowmen" when we saw him killed previously in "A Good Man Goes To War?" Huh? Wha happen?
Well, here's a brand new minisode that, uh, explains that plot hole.
EDIT: Oops! It's now blocked in the US by the BBC -- but you can view it for free on iTunes.
Hat tip to Life, Doctor Who and Combom!