If the 4th infralabial is larger than others on either side, the snake may be
If the 3rd supra labial is not touching eye and nasal shield, then look at the ventral aspect of head. If the 4th infra labial is larger than the others on either side, it is poisonous (krait) Ref: FORENSIC MEDICINE AND TOXICOLOGY Dr PC IGNATIUS THIRD EDITION PAGE 511
Cobra
Krait
Viper
Coral snake
Poisoning