I remember that all toads summoned by Jiraiya or Naruto were able to speak. I know that Tsunade's snail or Orochimaru's snake is able to speak, too. But what about the Ninken? I know that Pakkun can talk, but what about Kiba's Ninken and the others (I know around 3–4 dogs out of 9)? I know that the Pain summonings aren't able to talk.
Is there a rule that every animal can talk, or something like this?