2nd time lucky.
I thought I'd got it - to the extent I was sure I saw the leaf moving, as if it had a prisoner. Must have been an optical ilusion.
Anyway. - Today I saw the offending critter again, twixt 2 leaves of the vertical blinds. I clapped gently - BUT - not gently enough; seems I slew it rather than KOed it.
Remembering about keeping the triggers activated I had a "wain brave":-
What if, instead of tickling the hairs with a pin, I gently nip & release the sides of the trap; sufficient to move hairs, insufficient to damage leaf.
Seems to have worked, it's now fully closed.
I also heard the unlikey, but backed up, tale that a leaf stem could be used to propagate - we shall see.
There's another bud showing, other plant - I'll do it earlier to see if either work &/or if there's much difference.