This video from the USA says about itself:
10 July 2017
The Queen Crater Snail or Appalachina chilhoweensis is a rare snail and thought to be the largest native land snail in the eastern US – it is big and beautiful. This one was filmed at about 4,600 feet elevation in the Great Smoky Mountains munching on a large fantail fungus. This is a very wet and dark environment that does not get full sun in summer due to the dense forest canopy.
The video includes a closeup of their huge rasping “mouth” and its amazing ability to literally “swallow” its own head as a defensive maneuver when it bumps into a large beetle – perhaps some sort of stag-horn that was also eating inside the mushroom. When you see its “face” slowly reappear back out of its body you will be amazed. Combined with the music and the stunning beauty of this snail in action you may come to appreciate these wonderful creatures.