Achatina's are by far the hardest animals to escape on the island. Their insane movement speed is devastating to you and your dinos. These snails are also very powerful and will kill your gigas within, at least, 24 hours! The best thing to do when you see them is bola them and run.
Wanna hear something funny about snails? Stone Railings! (They can’t climb over them, but you can jump them at a sprint). This is funny to all survivors who use a Dino leash to restrain snails. Had a Bronto’s shadow disable my outdoor solar powered leash. Had to chase like 20 snails into the forest. One is still missing over a year later.