I made a response to this, but unfortunately, tumblr has a way of eating up anything more than 10 lines long, and it got a little lost. So, even though I’m not Hank, I thought I would make a full post explaining the science.
To understand why it’s happening, though, I’m going to have to quickly explain to you what is happening first.
Hopefully we all know that animation (and film) is just a collection of images, flashed in quick succession. The motion that we see, however, is pieced together in our brains, thanks to a thing called ‘persistence of vision’.
Persistence of Vision is caused by the lag in your brain. Seriously.
That brief instant it takes for your brain to understand what it’s seeing is the reason you’re able to watch movies. And we should be thankful for that brief instant.
Light comes into your eyeballs, and it’s crazy hectic data. There’s so much stuff happening all the time everywhere. And while our brains are good, they can’t process everything they’re seeing at light speed. Everything we perceive through our retinas is just light, bouncing off other things. We all know that, but it’s something we often forget.
The brain processes one instant of reality, then a snapshot of the next, and then the next, and so on, and pieces them together to create motion.
This is everything. This is your entire reality. The perception of instances blended together to form a delicious smoothy of senses.
For motion to be consistent, however, what it’s seeing needs to resemble what it was seeing the moment before. For example, for objectX to look like it’s moving, it needs to mostly be where it was the microsecond before, but slightly not.
Basically, you need to think about those ol’ claymations kids make, where the lego slowly edges fowards. You need to take that concept, and apply it to everything you’ve ever known and loved.
If objectX doesn’t overlap where it was before, it’ll look liked it appeared there out of nowhere or a whole new objectX. This is when the illusion of movement is broken. It doesn’t occur in live-action movies or reality as much, because it’s hard to break the illusion of reality when you’re in reality, whereas to create a realistic perception of reality, from nothing, on a screen?
Yeah, a little trickier.
In an industry setting, animators have to create at least 25 frames for every second of footage (FPS). And sometimes, in that 25 frames, animators need to have something move so fast on a frame, that it doesn’t overlap its previous self.
Their solution, as you probably know, is to stretch and contort their object in a way that’s not dissimilar from motion blur with cameras. Especially when you acknowledge that motion blur is everything that’s happening for that 1/25th of a second.
Again, a lot of this is common knowledge, but it’s a matter of how it all pieces together to work.
As you can see here, in figure A, the hotdogs are smoothly sliding out at a consistent speed, which means, if you were to mark each spot they were in every frame, the marks would make a straight line.
The intervals between each marking isn’t very much, because they’re moving quite slowly. The hotdogs are mostly overlapping themselves between each frame.
Now remember that the illusion of movement is all in your brain, where it looks for something that resembled the instant before, and projects trajectory into your concious.
The only reason you’re able to reverse the flow of hotdogs is because they look so similar, and because it’s literally all in your head.
When you make yourself think the flow of hotdogs is going into this fine gentleman’s pants, you’re making yourself believe that, in one frame, hotdogX moves almost a whole hotdog length down, instead of only a little bit of a hotdog length up.
And because it’s almost a whole hotdog length down, in just one frame, the distance of the intervals along the hotdog’s trajectory increases, which means it travels more distance in the same amount of time.
In that one instance of perceived reality (IPR)(Don’t use that anywhere serious, I just made that up), the hotdog moves 9 pixels, instead of 2 (approx.)(I’m not going to count them)
So, to summarize the answer to your question (aka TL:DR);
The reason why the ‘dogs fly into his pants faster is because your brain lag enables you to perceive motion through light (it likes things that look the same). And when things look the same, you can screw with your brain something hardcore.
When you force your brain to see things at different intervals, it can change how you perceive them.