Inez and Digit need to balance the scale with four numbers and gain access to the machine in order to save the bunnies from the dangerous cyberstatic. They balance five numbers with ease but realize they can balance only four numbers. They learn that removing the same weight from each side does not affect the balance of the scale.
The captain tells the squadron that he is expanding it to four members, which concerns all of the lieutenants. Lt. Purcell states that four is an unlucky number because it's not prime. He then defines a prime number.