Your favorite mystical "yes or no" supplement to Tarot?

I'm looking for a fun, eye catching, and/or visual way to have my clients get a yes/no answer to supplement their tarot readings. The way I envision using this is during the middle of spread/reading my client has a straight forward yes/no question come up. I like for my clients to feel empowered, so normally I will have them draw a card and tell them right side up means "yes" and reversed means "no", so they feel like they had some hand or power to determining the yes/no, and then I add a layer of information by interpreting the card itself that they pulled.

I'd like to do this same kind of thing without using a card - something like a coin flip that will always produce a yes/no outcome - but something more exciting and less mundane than literally flipping a fancy coin. I keep thinking of a "will it float" test, like they pull something from a bag full of similar objects, somee which float and some which don't, but of know way of actually knowing that (even by feel) unless its actually dropped in water. Or maybe they choose from a selection of powders and sprinkle some over a tea light candle, and if it flares up its yes and if not its no?

I don't really know what I would use for the float test. And for the fire test, when I'm doing many readings for people in the same room or repeatedly over time, how can I make sure they don't "figure out" which powders will flare and which wont.

Anyone have a favorite yes/no supplement divination tool, or thoughts and ideas about my float or fire tests?

EDIT: Since I wrote this post I started looking into it more - I've found natural pomice rocks float, because they're full of hollow holes that catch air, but some stones with smaller holes or have more dense interiors don't float. When I read amazon reviews of some natural pomice stones people were complaining they "ordered 12 and only 7 of them floated" which sucks for them, but is literally exactly what I'm looking for haha. By eye or by hand they wouldn't be able to tell which is a floater and which isn't, and if I have them reach into a bag to pull one out at random it would be more so, I'd imagine.

For the flames, I'm thinking I'd use tiny vials filled with either 1) baking soda + salt (no flame/extinguishes flame) or 2) sugar and powdered milk (flashes/flares). This way all the viles are white with mixed textures so the "yes" vials and "no" vials can't be distinguished easily. I could make black versions with black salt (no flame) or black salt + black coco powder (flare).

I kind of feel like I'm on to something here lol I might try both the float and the fire to have a fire/water duality element to the readings. If wands and/or swords are dominant in their reading(s) they go with the fire test and if cups and/or pentacles are dominant they go with the float test?