Futurama: When Did The Enlarging Ray First Appear & Why Doesn't Anyone Remember It?
Contains spoilers for "Futurama" Season 11, Episode 4 — "Parasites Regained"
The tweaking of science-fiction tropes has become common on "Futurama." To wit, during "Parasites Regained," Fry (Billy West), Zoidberg (also West), Bender (John DiMaggio), and Leela (Katey Sagal) use Professor Farnsworth's (West again) Enlarging Ray — which normally resizes matter to oversize proportions — to shrink down and do battle with the worms infesting Nibbler (Frank Welker) and threatening his portentous intellect. All it takes is a simple flip of the lens to make such "Fantastic Voyage"-like magic possible.
When Farnsworth introduces the ray and asks the crew if it seems familiar to any of them, he receives a resounding "no" from one and all. However, for fans of the show, it's quite a notable invention; Farnsworth previously used it to enlarge Zoidberg for battle after Bender became an oversize robotic terror threatening the very existence of New New York.
So why doesn't the Planet Express crew remember the Enlarging Ray? Because the Professor first uses the device in an "Anthology of Interest I" story and nothing that happens in "Anthology of Interest I" affects the events that take place within the main continuity. Thus, the characters wouldn't remember having encountered it before. And — when one reflects on some of the things that take place in "Anthology of Interest I" — that's a good thing.
Anthology of Interest I definitely doesn't count as a linear part of Futurama's story
"Anthology of Interest I," one of the 30 best "Futurama" episodes, uses an anthology format to explore alternate worlds featuring the central characters. Each of its three stories is used as a vehicle to take the show in some pretty wild directions storyline-wise — including "Terror at 500 Feet," in which an enlarged Zoidberg ultimately kills a 500-foot-tall Bender. In fact, death happens pretty indiscriminately to the central cast, with Leela murdering the entire crew in the story "Dial L for Leela" after she decides to be more impulsive.
With that in mind, it's an excellent thing that what happens in these stories doesn't affect what happens on "Futurama" proper. After all, that's what makes the show's anthology episodes so great. And it'd be a whole lot less fun if characters could remember them.