The following Incredibly Lame Pun from the iron episode - (paraphrased) "The iron pyramid is connected to an alternating current from the mains as well as a direct current from a battery. We're using AC/DC because it's heavy metal."
An enormous pair of scissors has appeared.
Thanks Tchaikovsky. Thaikovsky.
"Probably about ..5.05 Mg" (read point-point five point oh five microgallons)
The "Little Mouse" song.
The Incredibly Scary Picture from series 2. Great effort is taken to point out before it's first appearance how scary it is, with a stock "those of a nervous disposition look away now" only for the incredibly tame picture (A bear and a skeleton) to appear late. The image continues to appear at random throughout the rest of the episode.