Ah, all right. Did I miss something, or since when is that hellhound called Cerebrus?

Anyway, the hellhound itself won't settle the fight.
Since Kishi never draws a summoning uniformly in terms of size it's hard to say how much bigger Manda is - but it's clear that he is way bigger. Snakes are known to devour huge pray. If Tsunade hadn't interrupt, Manda would've even
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. Jiraiya used a stomach to stop the dog, so it should work in this case, too. If the dog ist directly devoured, without being otherwisely attacked, it can't split up. Even if it would manage to do so; Orochimaru has more than enough snakes to keep the dog occupied.