Snake Pokemon

Ekans and Arbok are the Poison Type Pokémon 

but there were fictional Snakes. 

Ekans was Snake spelled backwards 

and Arbok was Cobra spelled backwards. 

Ekans looked like a Rattlesnake 

with a Rattle on its Tail 

and Arbok looked like a King Cobra 

with Markings on its flattened Hood.
Rattlesnakes and Cobras are poisonous Snakes.