Ok, kind of a weird title, but it'll make sense I promise.
Something I've always been confused by is how the follower "knows" how to turn around on the 3 & 4 of a open-starting swingout. It's not led by the leaders' hand and the momentum from the 1 & 2 has us moving past then in a linear fashion. Diagnosing with my practice partner the other day, he reminded me that a subtle "rule" (I don't really like using that term but it's the best one I have right now) of the dance is that you're generally trying to face the others' sternum. This was an "aha" moment for me that makes the 3 & 4 make sense. As I go past the lead on 3 & 4, if I don't turn my sternum will move away from his rather than towards his. This applies in other moves too from a tuck turn to a pass by, even though those moves have stronger leads.
There's probably another way to reason this out as well with "frame". If I keep moving past my lead linearly, at some point (assuming he doesn't move) I'll need to rotate in order to hold my frame shape. It may be that thinking about it via the sternum lens is just easier for me right now where as frame is a more universal concept and therefore may be a "better" way to view it in the future.