Poskok (jumper) is a legendary mystery snake of Croatia. It is said that the snake could jump into the air even as much so as 2 meters and attacks it's pray by jumping on it's head from trees and strangling it.
No snake known to science has the ability to jump into the air from the ground. At best, snakes can lunge while striking.
Physical description: Length, 2–3 feet. Thickness, 1.5 inches. Gray to dark reddish-brown color and has a horn on the nose.
Behavior: Venomous. Aggressive when disturbed. Can jump a distance of 5 feet, moving 3 feet into the air.
Distribution: Dalmatian Coast, Montenegro...
- It could be one of the Yugoslavia’s whip snakes: the Balkan whip snake (Coluber gemonensis), the Large whip snake (C. jugularis), Dahl’s whip snake (C. najadum), or the Western whip snake (C. viridiflavus). These nonvenomous snakes are similar in size and color to the Poskok. As plausible as this theory is it still doesn't explain the jumping and the attack method.
- It could be one of the area’s vipers: Orsini’s viper (Vipera ursinii), the Common viper (V. berus), or the Nose-horned viper (V. ammodytes). The nose horned viper matches Poskok's description the most, but can't jump into the air.
- Snakes seen on bushes or low trees are sometimes presumed to have jumped there. It still doesn't explain people seeing Poskok jump into the air and the attack method.
Sources: Maurice Burton, More Animal Legends (London: Frederick Muller, 1959); Karl Shuker, Fortean Times, no. 123 (June 1999): 46., http://www.beastofbala.com/files/25.pdf Mysterious cretures: Guide to cryptozoology, Croatian Legends...