Put simply... when THIS happens.
Skip to 2:00 and watch what I say.
Other videos, including
This one in the series have odd little things. Like what's happening in a lower corner be duplicated or moved to someplace else on the video. Apparently, Yukari doesn't like my videos, because she's been opening gaps all over them.
A portal fan, upon viewing them, would ask: "Why the hell was an Aperture Science Handheld Quantum Tunneling Portal Device used in this thing?"
Us touhou fans want to know: "Why has Yukari opened all these gaps in my video?"
The even stupider thing? I DIDN'T DO IT ON PURPOSE. It just happened. So if you want to know how it was done, all i can say is i was using XSplit and FCEUX to record.
The rest... just happened.