$ perl -MEncode -e'printf "%04X\n", ord decode "UTF-8", "\357\277\275"'
FFFD

##</code><code>##

$ perl -MEncode -we'print decode "UTF-8", "\215"' | od -c
Wide character in print at -e line 1.
0000000 357 277 275
0000003

##</code><code>##

print $mech->response()->headers()->as_string();