It's like they used to do in the Middle Ages. If an accused witch floated when thrown bound into the river, then she was guilty and later hanged. But if she sank to the bottom, then she was innocent and thus exonerated. Either way, she died.
Salve, Regina, Mater misericordiae
Vita, dulcedo, et spes nostra
Salve, Salve Regina
Ad te clamamus exsules filii Eva
Ad te suspiramus, gementes et flentes
O clemens O pia