$ perl -Mre=debug '1 =~ `'
Freeing REx: `,'
Compiling REx `1'
size 3 first at 1
   1: EXACT <1>(3)
   3: END(0)
anchored `1' at 0 (checking anchored isall) minlen 1
Guessing start of match, REx `1' against `1'...
Found anchored substr `1' at offset 0...
Guessed: match at offset 0
Freeing REx: `1'
##</code><code>##

$ perl -Mre=debug -e 'BEGIN { close STDERR } 1 =~ 1'
Freeing REx: `1'
##</code><code>##

re.pl:
package TrapRe;
sub TIEHANDLE {
    my $class = shift;
    my $fh = \do { local *HANDLE };
    bless $fh, $class;
}
sub CLOSE { close $_[0] }
sub READ {}
sub READLINE {}
sub GETC {}
sub WRITE {}
sub PRINT {}
sub PRINTF {}
sub BINMODE {}
sub EOF {}
sub FILENO {}
sub SEEK {}
sub TELL {}
sub OPEN {}
sub DESTROY {}
sub UNTIE {}

package main;
use re 'debug';
BEGIN { tie *STDERR, TrapRe; }
1 =~ 1;

$ perl re.pl
Compiling REx `1'
size 3 first at 1
   1: EXACT <1>(3)
   3: END(0)
anchored `1' at 0 (checking anchored isall) minlen 1
Guessing start of match, REx `1' against `1'...
Found anchored substr `1' at offset 0...
Guessed: match at offset 0
Freeing REx: `1'