Let's say there's a quite thick flipbook that all frames of a video are bound page by page. If you just rifle through it, the original video will be just played. Slit-scan intrinsically means slicing the flipbook diagonally. [...]
I think the name of "slit-scan" makes people confused. It's rather appropriate to call it "time displacement" just like the name of AE's effect because this technique actually means displacing a cross section of "world volume" (like a flipbook, it is an imaginary 3D cube consists of 2D image + 1D time) along with "time axis".