Although Season 2 of Sherlock has yet to air in the U.S., those of us who do not fear spoilers have gleaned much about it. (This post is spoiler-free, the links, however, not so much...)
Remember my post on P.R.O.B.E., the straight to video spinoff of Doctor Who featuring Caroline John reprising the role of companion Dr. Liz Shaw? Well, I seemed to omit the fact that P.R.O.B.E. was written by Mark Gatiss, and the episode Unnatural Selection bears, shall we say, a family resemblance to the Gatiss-penned script for The Hounds of Baskerville.
Note the parallelism between the series title and acronym P.R.O.B.E. and the acronym H.O.U.N.D.
Gatiss may not boast about P.R.O.B.E. (he is cited as having "said in a 2004 interview that he would not authorise their re-release as regarded them as having been a learning exercise"), but clearly he hasn't forgotten the series altogether.