Modder TheZZAZZGlitch has discovered that it's possible to dump and recreate a GBA ROM by crashing the game and recording the sound that plays after an hour and a half.
While that makes it sound like an easy process, actually getting the ROM recreated and working took TheZZAZZGlitch quite a lot of time – and they had to cook up special hardware to do it.
Even so, by taking multiple recordings and tinkering with the code, the modder could eventually get a successful, accurate dump of the game data and boot it up.
"Turns out, the GBA crash sound is just the console playing its entire address space as sound data," they explain. "If we have a clear recording, we can convert it back to actual bytes, thus dumping the RAM and ROM. Note - this is hardly a ready-to-use solution and requires a lot of tuning, depending on the source data format."
You learn something new every day.