This would be more historically accurate:

use strict;
use warnings;

use File::Basename qw( basename );

sub usage {
    my $prog = basename($0);
    print(STDERR "usage: $prog suspect\n");
    exit(1);
}

sub witch_test {
    my ($suspect) = @_;
    return 1 if $suspect->float();
    return 0;
}

my ($suspect) = @ARGV
    or usage();

my $is_alive = ($is_witch) = eval { witch_test($suspect) ?1:0 };

if ($is_witch) {
    if ($is_alive) {
        print("Burn her!\n");
    } else {
        print("God's will has been carried out\n");
    }
} else {
    if ($is_alive) {
        die("Assertion error: Need better witch test\n");
    } else {
        print("What a *cough*tragedy*cough*\n");
    }
}
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Update: Fixed negated logic mentioned by JavaFan