Flexi Rex with movable jaw. Just give it a bite!
Close the mouth, and then open it.
Repeat the above procedure until the jaw is free to move.
Jaw gaps 0.30mm(da Vinci Jr.1.0A & CR-10S) and 0.50mm(da Vinci mini w) are suggested for 100% printing.
Try test-gap things (Rex pencil top https://www.thingiverse.com/thing:3263585 or Rex keychain https://www.thingiverse.com/thing:3395707) first to ensure the acceptable jaw gap of your machine.
Larger gap can be used for smaller-scaled printing, and smaller gap can be used for larger-scaled printing.