the limited computational capacity of the PlayStation 2. While the basic movements of the character models were animated by hand, their physical interactions are simulated in real time by the game's physics engine. The generated data is input to the IK system to animate the joints of a model, and, by extension, its entire body. In the process, the system estimates the displacement, angle and the direction of the finalized motion, and the model is positioned in the environment according to these calculations. As a result, predefined animations are blended with physical effects to create lifelike character movement: for example, the player character behaves like a swinging pendulum as he hangs onto a colossus while it tries to dislodge him. As applied to the protagonist's horse, the technology enables the character to adjust its posture when on uneven surfaces for added realism, a feature that extends to the colossi. With regard to the colossi, Team Ico were keen to ensure that their motions were plausible, and strove to accurately convey the massiveness and energy level of the creatures. The colossi were programmed to react to the occurrence of specific player-driven events within one of the "sensor" areas set by the artificial intelligence (AI) of the enemies across their surrounding territory. For example, if the player character is at ground level and approaches an armed colossus from the front, the creature brandishes its weapon against him. As opposed to a hard-coded program, the colossi's AI could be fine-tuned for each of the game's scenes. Team Ico also developed AI-enabled movement algorithms for protagonist's horse, which was conceived as a realistic representation of its real-life counterparts. This solution allows the horse to occasionally ignore the player's commands and to be proactive in order to avoid visible sources of danger within its surroundings. However, Ueda admitted that the team had to seek a balance in how often Agro did not respond to player input so as to not sacrifice playability in the pursuit of realism. Kaido admitted that Team Ico's ambitions for the game were partly unimplementable with the PlayStation 2 hardware, and that the team "[lost] sight of the cardinal rules of game design" several times during production. One of the issues that caused them to discard assets already added to the game was the variety of the colossi. Ueda initially intended to incorporate 48 colossi in NICO, but their amount was