"Looking back now, Ico was more or less about the cooperation between the boy and Yorda, a non-playable character," Ueda said via translator. "We've taken elements from that. Looking back at Shadow of the Colossus, it was more about the dynamic interaction with the giant creatures."
We've already seen a little of this in The Last Guardian demo. Trico is a massive, griffin-like creature that accompanies the game's young hero and can't be controlled by the player — though he can be guided through verbal commands.
Ueda said that the player is supposed to read the situation they've been put in, and try to use each character's strengths to move through the game's strange prison. The boy is weak but has a clever mind; Trico excels in strength and size, but is only a beast. As to what kind, that's sort of up to interpretation. Ueda called it a mix of a dog, a cat, a bird and perhaps even more — the only goal was to make Trico feel believable. Speaking about his past work, Ueda said that his work with Ico and Shadow of the Colossus has always focused on a sense of height. The Last Guardian is much the same, though Trico acts as ... well, a guardian.