A Viper is an orange venomous snake with black stripes and horn on it's nose.
They are extremely aggressive, attacking any living creature, including other snakes. When they attack someone, the adjective poisoned is given. This snake will eat smaller animals (mouses, frogs, lizards etc), any type of meat and organ.
In Scribblenauts Unlimited they became much more friendly, only attacking in self-defense. The rattlesnake is protective towards other snakes, becoming hostile if you attack them. Clicking on them gives the Pet option, selecting makes the rattlesnake play the Fiddle animation while expressing the emotion.