$ perl -CS -e'
   my $s = "\xC3\xA0\xC3\xA1\xC3\xA2\xC3\xA4";
   printf("Before first decode: %1\$vX [%1\$s]\n", $s);
   utf8::decode($s) or warn("First decode failed.\n");
   printf("After first decode:  %1\$vX [%1\$s]\n", $s);
   utf8::decode($s) or warn("Second decode failed.\n");
   printf("After second decode: %1\$vX [%1\$s]\n", $s);
'
Before first decode: C3.A0.C3.A1.C3.A2.C3.A4 [àáâä]
After first decode:  E0.E1.E2.E4 [àáâä]
Second decode failed.
After second decode: E0.E1.E2.E4 [àáâä]