I'm having a little trouble remembering how to draw the kanji for SEPARATE. The story helps me remember the The Heisig explanation for the primitive element he calls BOUND UP offers no clues to differentiating the long and short versions of the second, left-hand stroke of that primitive. I'm just past 450 kanji, so far, and I can only recall two appearances of the elongate version of BOUND UP: TEN THOUSAND and SEPARATE. Now, possibly, Heisig intended to clarify this when he says, "If you have trouble remembering when it serves as an enclosure (with the hook) and when not (without the hook), you might think of the former as a chain and the latter as a rope." If so, I don't think the wording works.

I've not seen any version of BOUND UP that I would characterize as "without the hook." They all have a hook. The first stroke of the primitive is always hooked. He does, however, use the "rope" distinction in the story for SEPARATE.

So, perhaps, the explanation for BOUND UP should read, "If you have trouble remembering when it serves as an enclosure (with the short stroke) and when not (with the long stroke), you might think of the former as a chain and the latter as a rope." That might work.

I wouldn't worry about this one too much, as you'll be seeing "separate" all the time in Japanese later on. I actually had forgotten that that small primitive under mouth is called "rope". My stories only come back to me now in visual flashes. I'd say stick with the Heisig story, it worked for me. That little "rope" primitive at the bottom of "ten thousand" is not very frequently used as a solo-radical like in 別 (mouth+rope), but it's usually in the 万, or 方 form when combined in a bigger kanji. So my advice is to learn 別 as an oddity, then learn 万, and 方 really well as primitives.

I think I just learned that through muscle memory/spaced repetition. I probably learned most of the variations of primitives in that way.