c:>perl -d devel.pl

Loading DB routines from perl5db.pl version 1.23
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(devel.pl:3):     my $a = undef;
  DB<1> n
main::(devel.pl:4):     Dump $a;
  DB<1> n
SV = NULL(0x0) at 0x1829ce0
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY)
main::(devel.pl:5):     my $b = \$a;
  DB<1> n
main::(devel.pl:6):     Dump $a;
  DB<1> n
SV = NULL(0x0) at 0x1829ce0
  REFCNT = 2             ###<----- correct count
  FLAGS = (PADBUSY,PADMY)