Unbroken
A tone with holes cut in it. Fill the holes with the right noise and you hear the tone continue through them, sound your speaker never made. WIZ measures the level where your ears start inventing it, then the rule that decides whether they are allowed to.
Headphones if you have them, and set your volume with this: a plain 1000 Hz tone, three seconds, nothing hidden in it. Comfortable and clearly audible, not loud.
Both buttons play an identical tone with two quarter second stretches cut out of it. The tone file is the same in both. The only difference is what sits in the holes.
Nothing was added to the tone in the second one. It is still missing exactly the same half second in total. Your hearing built the missing part and handed it to you as sound, seamless, in real time, and knowing this does not switch it off. Try the second button again now that you know.
The interesting question is not whether you can be fooled. It is when your hearing is willing to do it, because it will not do it for just any noise. Sixteen trials find the level where the gap closes for you. Thirteen more find the rule.