CME launched its futures contract on 12/17, which enabled traders to short BTC, previously not possible. The only supply on the mkt was from traders who were long BTC. Now traders can sell it w/o actually owning the coin (for the novice traders out there). I don't think it's a coincidence that this now marks the top of BTC appreciation; there is a two-sided market now, like all other securities. I asked this question on twitter, "if biotech stocks weren't able to be shorted, what would the average mkt cap be?" Answer: A lot higher than it is right now!! BTC may be returning back to earth. Be careful if other coins get listed for futures trading.