The episode had the working title of First Contact (Number 122). This was a reference to the number of occasions on which UNIT had encountered alien lifeforms, ostensibly, always for the first time.
The Doctor's sonic sunglasses show that Bill is a 26 year old female who weighs 130.2 pounds, is 167.6 cm tall, has a heart rate of 79 bpm and a body temperature of 37.6 degrees C.
Doomsday Clock update: As of January 2020, it is set at 100 seconds (1 minute 40 seconds) before midnight; which is the closest to midnight the clock has ever been set since it's foundation in 1947. In the immortal words of P.F. Sloan, "We're on the eve of destruction."
"Enzyme EC 31" tank seen in the lab is probably based on the real Enzyme Comission (EC) number system for classifying enzymes based on the chemical reactions they catalyze. However the real codes are in the form of four numbers separated by periods.
This title has the longest word count for an episode, with eight words. By character, however, it is not the longest. That title goes to The Doctor, the Widow and the Wardrobe (2011), with 32 characters over Pyramid's 28.