Reversing is the art of rewinding video or sound. Some video editors happen to have this as an option-- WMM isn't one of them.
A load of videos tend to use reverse as a way of finding secret messages. They're often very subliminal and risque to the children. After viewing the video, tell yourself: Innocent kids show; or a disgusting piece of art?
Styles of Reversing
Another technique of reversing that involves playing a clip forward, then playing the same clip backwards, which became more widely used around 2009 or so. Also used for creating Sus sounds.
In Windows Movie Maker
Movie Maker does not have a "reverse" effect by default, so one has to do it manually. How so? One takes the video, chops it into tiny, frame-by-frame pieces, and puts them in the reverse order. The effect is imperfect and jerky, though to some, this adds to the humour.
In Other Editing Programs
It's as easy as just clicking on the video clip you want to reverse and then apply a "time-shift" effect. Modify the exact details of the time-shift so that "reverse" is one of them.
Sony Vegas: right click on the video and audio then select Reverse!
VideoPad: go to effects, select speed, and then select "Play backwards"
Premiere: Right click, Then to the Speed/Duration menu and check the "Reverse Speed" tick box.
There is no such thing as a dictionary featuring reversed words. But, someone is in the process of making one. Until this author finds every word, the project will have an unknown release date.