This surprise mimic chest storage area can be opened by lifting the bottom teeth that is locked in by 4 notches at the corners. When putting the bottom teeth back in make sure to press it down until it clicks and snaps in to the notches at the corner. 

 

The top teeth can also be removed to change the "surprise mode" of the chest. In order to change "surprise mode" to "normal chest mode" you just need to unlatch the rubber band from the original location and use a longer rubber band to go across side to side. Any thin rubber band will do, if its too short try linking it together.