I think it's an improvement. Obviously Seviper is based on a viper, though I didn't do that much research and the 'claws' are, I belief, only found on anaconda's. In any case, not on vipers. Zangoose = mongoose. Duh! Except that they don't look like mongoose. Shorter snout, huge forearms, fluffy tail, fluffy ears... But still, I think they eat each other. Whoever wins the fight, gets the meal. Seviper are up to three metres long, but Zangoose are 'only' 1.4 metres, so I imagine the Zangoose jumps the Seviper, wounds it as much as possible and then gets the hell away as fast as he can. Wounded Seviper can't follow as quickly, dies, gets eaten. The other way around is pretty much the same: Seviper bites Zangoose from ambush, waits for venom to take effect, eats Zangoose. They probably eat the same prey besides each other, hence their rivalry. I dunno, I have to admit I didn't actually make anything up for these two.

Again, thanks to  Ookami-girl for the idea.