How to summon a different animal using Kuchiyose? As we know, every ninja needs to sign a contract to summon an animal. However, Sasuke suddenly summoned a hawk, after summoning snakes all the time.

How can someone change the animal he summons? 


   I know that with Keiyaku Fūin, the contract can be broken, but I guess that works a little bit different, not?
Kuchiyose is a highly controversial jutsu, cloaked in mystery.

At the beginning of the series, Naruto is presented with the frog contract scroll. In which he signs with blood, thereby validating the contract. From that point onward, he can summon frogs. The same happens with Jiraiya (who's name is earlier on the list).

Orochimaru has a tattoo on his right arm, on which he smears the blood required for the summon.

Madara Uchiha was seen summoning the Kyuubi after taking control of it, and using it in battle against Hashirama, seemingly without a contract.

Tobi was seen using the same technique after he unsealed him from Kushina.

As for the Rinnegan's Animal Path, it's very likely to assume that the summoned animals are some sort of zombies as well (much like the Rikudo no Jutsu's bodies), as they have the Rinnegan and the Piercing (and doesn't talk at all).



It seems that a general contract with the species, or control over the specific creature is enough. If there's a contract, both sides can freely summon each other (As seen by Shima's reverse summoning). If there isn't one, it probably takes the "consent" of both sides for the technique to work (Or, the forced consent, in the case of the Kyuubi).



The technique is very unclear in nature. It's a space-time ninjutsu, which on itself is a mystery, and very little is known about it. We don't have much more detail than that.