Board Thread:Wiki-Related Discussion/@comment-2153169-20150201203847/@comment-24950802-20150201222735

But he also said that "Smash the Mirror" is two episodes that aired together. The composite episode's production code is 408 (408A and 408B, it seems), but like I said, a production number is not an episode number. You can say 408B is the 9th episode of the season still. "Fall" (409) would be episode 10, and so on.