An arrow mark or bird foot mark on the centre of head suggest it is
If the head is triangular and covered with small scales, it may be poisonous(viper). If there is an arrow mark or bird foot mark on the centre of the head, it is poisonous (saw scaled viper) Ref: FORENSIC MEDICINE AND TOXICOLOGY Dr PC IGNATIUS THIRD EDITION PAGE 511
Pit viper
Saw scaled viper
King cobra
Krait
Poisoning