Identity Crisis

"So was Donna right?" Martha asked Ood Sigma. "About how a species which
carries its brain has to be *able* to trust everyone it encounters, and
therefore assumes it *can*?"

"Mostly," Sigma replied. "There is another factor. Humans can make
informed decisions as to whether or not to trust another human based on
past actions. This, in turn, influences the decisions made by that human.
The Ood cannot do this, so either we must be trusting of all others, or
untrusting of all others. And a completely untrusting species would never
have survived at all."

Martha frowned, "Why can't you make decisions about other individual

"Because we never know which Ood performed past actions," Sigma
explained. "You see, unlike our cousins on the Sense-Sphere, we never
invented sashes..."

So I looked, and behold, a pale horse.
And the name of him who sat on it was Death.
And the name of the horse was Binky.