Difference+between+poisonous+and+non-poisonous+snakes Points. Poisonous snakes. Non Poisonous. 1. Belly scales. Large : They cover the entire breadth of belly. Small : They never cover. 2. Head scales. a) Usually small in vipers. b) May be large in pit vipers. c) Cobras and Coral snakes where third labial touches the eye and nasal shields. d) Kraits ,where there is no pit and the third labial does not touch the nose and eye. Are usually large with exceptions as outlined under poisonous snakes. 3. Fangs. Are hollow like hypodermic needle. Short and solid. 4. Tail. Compressed. Not markedly compressed. 5. Habits. Usually nocturnal. Not so. 6. Teeth bite marks. Two fang marks with or without marks of other teeth. Two fang marks with number of small teeth marks.