Snakes with venomous fangs.
Many snakes with long fangs can fold them back.
But a King Cobra's fangs look pretty long. Why can't we see them when their mouths are closed? Their fangs cannot fold back.
Outside United States
Thank you for your question. There are two groups of front-fanged venomous snakes. The solenoglyphous group has fangs that are hinged and lay against the roof of the snake's mouth protected by a membranous sheath when not in use. Snakes in this group include vipers, pitvipers, the Australian deathadders and the African molevipers. When the snake does strike at prey, for example, the fangs swing down from the roof of the mouth, the snake opens its mouth almost to 180 degrees and jabs the fangs into the prey. It then injects the venom, withdraws the fangs and they fold back up towards the roof of the mouth. It takes much longer to explain this process than it takes the snake to actually complete the strike and bite. Research has shown that some rattlesnakes can lunge forward approximately half a foot in 70 milliseconds. In comparison, the blink of an eye takes approximately 200 milliseconds. Fang length in this group can be quite long. In the genus Bitis, a group of African vipers, the Puffadder (Bitis arietans) can have fangs up to 28 mm long, and the fangs of the Gaboon Viper (Bitis gabonica) can measure up to 30 mm.
The other group of front-fanged snakes is called the proteroglyphous group. Members of this group are in family Elapidae (cobras, mambas, coral snakes, seasnakes). In this group, the fangs are located in the front of the mouth, but they are fixed in the downward facing position, just like the rest of the snake's teeth. As a result, the fangs of snakes in this group are not very long. Otherwise, these snakes would require a deeper mouth cavity, so the fangs would not puncture the floor of the mouth. The King Cobra (Ophiophagus hannah) has fangs that measure from 8 - 10 mm. Other species in this group have even shorter fangs.
I hope this answers your question, and thank you for contacting Ask an Expert.