So the big question is a biological one more than anything else: HOW could an existing fish species like the eel develop into such a gigantic and different form like the lindorm type?
Of all the 48 testimonials published in 1886 from Småland county, a major part described animals firmly on land, in bushes, among stones and sun bathing like a snake, including hibernation together with normal adders and grass snakes. It is known that normal eels can migrate over land for some distance but the lindorms seem to behave like lung breathing animals. Although it may be of a type skin breathing in this case, together with an abnormal type of gill breathing. The described "folds" or "sacks" on the side of the head may be enlarged gills perhaps. Just like an angry dog, the lindorms raised the scales/hairs on the back when irritated by humans. When attacked by humans, they could raise their body over a meter from the ground, with a hissing sound.
This a first class enigma.