A tiny spark of flame that acts as a pyrausta's heart beats within its chest. Whenever a pyrausta takes cold damage, including damage from environmental cold, its little heart stalls. Its regeneration does not function until the end of its next turn and it must make a DC 11 Constitution saving throw. On a failed save, it must use its next action to re-ignite its heart, or it will take 1 point of cold damage at the end of each of its turns until it does.