Continuity mistake: When Piper reveals herself as the killer in the dock, you can see her dropping the mask and shortly after, removing her poncho and drop it on the floor as well. In the next shot from the side of the dock where you can see Piper and Emma face to face, the mask and the poncho are no longer on the floor. (00:32:20 - 00:33:10)David Pinhal
Trivia: Originally, the new "Ghost Face" mask was meant to be made out of human flesh that was being stretched over the killer's face, hence it distorts and resembles a "screaming face" like the original Ghost Face mask. This idea was dropped relatively early in filming. However, several scenes had already been filmed with the killer for the pilot, so in some shots, the mask is actually a CG model that's been added in over the original. (Though thankfully it's hard to tell which scenes have the digital mask).
Trivia: The producers decided not to use the iconic original "Ghost Face" mask, but instead create a similar-looking-yet-decidedly-different mask in order to help the series stand on its own. This idea was met with some controversy, including from Wes Craven, whom directed the films upon which the series is based. It was eventually revealed that the original "Ghost Face" mask will make a return to the franchise in the third season, which will be a "light reboot" that starts the series in a new direction.