Small and compact at rest, the Shockjaw stretches nearly three times in length when delivering a bite, which not only drains blood but stuns most prey with a powerful jolt of electricity. When sufficiently agitated, energy arcs visibly between its teeth.
This design is based on the real-world Rattrap fish or loosejaw, and has been only subtly exaggerated:[link]
(a beautiful, scientifically accurate painting)[link]
(a dead specimen)
I'll admit that the electrical ability came only from trying to think up a jaw-related name and coming up with nothing else.