Usually, but not always with fast moving momentum stocks like TWTR. The initial movement is triggered by algorithms that try and figure out if the earnings report was good or not. I remember an absolutely wild Facebook swing after an earnings statement that went from huge up to down the next day (once it was mentioned on the conference call that teen usage was down).

There are going to be a ton of sellers tomorrow (if I had any shares I sure would), it will be interesting to watch. You know that some of the bears who got squeezed this afternoon are going to double down and be back on the hunt tomorrow.