Originally posted by: kupalmaru
The frog does not go from small to big.

Remember when Naruto summon the frog when he was falling on the cliff. It was a big chakra or something that resemble a frog. Then the big chakra it turn into a frog.

Just watch that episode.

edit:

I agree with some people, it's all about the chakra. When Naruto summon Gamabunta(you can see a large amount of chakra forming in a shape of a frog). It will be impossible if that big chakra turned out to be Gamachi. LOL
maybe its wif the contract thing... no contract no summon... not enuff chakra no big big frogs...