Caching component references

Repeatedly recalculating a value is a common mistake when scripting in Unity, and particularly when it comes to the GetComponent() method. For example, the following script code is trying to check a creature's health value, and if its health goes below 0, it will disable a series of components to prepare it for a death animation:

void TakeDamage() {

  Rigidbody rigidbody = GetComponent<Rigidbody>();
  Collider collider = GetComponent<Collider>();
  AIControllerComponent ai = GetComponent<AIControllerComponent>();
  Animator anim = GetComponent<Animator>();

  if (GetComponent<HealthComponent>().health < 0) {
    rigidbody.enabled = false;
    collider.enabled = false;
    ai.enabled = false;
    anim.SetTrigger("death");
  }
}

Each time this poorly optimized method executes, it will reacquire five different component...