Under unfavourable conditions Achatina snails can "den up" (come to hibernation).
Achatina snails seal up the mouth of shell by lid of stark muscus. This cover is rather thick and solid. It looks like fragile plastic.

  An adult snail can be in such condition for months.

  If you moisten the shell, Achatina snail wakes up in 10-30 minutes, pushing out the lid.

  After awakening snails begin to guttle and drink to recreate.