Found a tape in our ZX Spectrum collection that we didn't know what it was.
Put it into the tape deck, played it into the Spectrum. Spectrum caught the loader, even gave us a program name, gave us the loading bars, tried to load. Would never succeed, though.
Was just going to throw it in the bin, but by accident pulled out the earphone cable from the tape player.
Turns out, it was my brother and I messing about with the tape recorder downstairs while - in the background - dad was trying to load Nonterraqueous into the Spectrum.
Just the background noise of the loading tones, behind us recording all kinds of nonsense and fake news reports, etc., was enough for the Speccy to be convinced it heard a leader and try to load the game.
I always wondered if - if you were able to clean up the signal enough - you'd actually be able to load the game from that historical recording.