Misc: how many pints of blood in the average human body?

Questions

Fish travel in schools, whales travel in pods or ----------?

Because birds carrying messages were often killed in flight by hawks, medieval Arabs made a habit of sending important messages ----------?

Many corals receive nourishment from algae which grow inside their ----------?

---------- feel safest when they are crowded together, hundreds in a group.?

Because it is continually losing body heat, the ---------- must keep moving to stay warm. If inactive for more than a few hours, the animal will lose enough body heat to freeze to death.?