Hazards troops might face in the tunnels include booby traps, pressure release bombs, punji stakes, snake traps( VC would tie a deadly bamboo pit viper which has a hemotoxin venom to ceilings,bushes so that they bite an unaware enemy in the neck, face or hands. VC would also hide snakes in sacks, crates etc), and mines.
As well, enemy combatants ambushes. Apart from regular ambushes, some tunnels had special holes in the walls for VC to thrust stakes through them and impale any intruder.
Sometimes VC would lay in wait on trap doors and entrances and wait for soldier to emerge and then kill them with stakes, shots, knives.
Some non fatal dangers included bat swarms, spiders and the notorious Vietnamese fire ants.
Not to mention one could also get lost in the tunnels.