As I was early in the game, one of the first creatures I saw by the Swamp was this Sluggish Creature. I had to crouch and use my new bola. I swung it at the Achatina and it did not look harmed. I then had to trap it, until a Sarco came up and ate me and my Slug. Later, I had found another one, this time with no Sarcos nearby, and found that they don't eat meat. I tried to tame it with Cakes, because after taming an Ovis I knew a few creatures ate them, and claimed it! Be wary, these creatures are some trouble to handle.
If you are considering breeding these, go slam your hand in a car door a few times. It will be much less painful. Literally one veggie cake per percent of growth....and it grows slow.. Digests roughly one point of food per second, so feed a cake about one for every 7 mins (during event boost) and it will gain one percent of growth.