Fang blennies aren't likely to jump from normal daytime activity - they're pretty brave and curious fish. However, they tend to sleep vertically against the glass in the corners of the tank. If startled while sleeping, reflex may kick in causing them swim quick ... which means upward and out of the tank. (I lost one when a hall light got turned on in the middle of the night and spooked it. Found it on the floor later that morning.)
Also, 3 fang blennies in a 50g isn't advisable. A mated pair would be fine. But, while they're great with most other fish, they're aggressive toward other fang blennies.
Also, 3 fang blennies in a 50g isn't advisable. A mated pair would be fine. But, while they're great with most other fish, they're aggressive toward other fang blennies.