As formatting marks. Good catch. The first argument of printf (not counting the file handle) is the format string. % is a special character in the format string. A spate of vulnerabilities that surfaced last year were caused by user text being used as a format string.

If you do need to use printf for whatever reason, there's a couple of alternatives:

printf BIDWATCH '%s', $part->bodyhandle->as_string;
[download]

$s = $part->bodyhandle->as_string;
$s =~ s/%/%%/g;
printf BIDWATCH $s;
[download]