This ($b) is a scalar ref: my $a; my $b = \$a;; this ($c) is a reference to a reference: my $a; my $b = \$a; my $c = \$b;

A REF(0xxxxxx) is a reference to a reference. Ie. Above $c is the same as my $a; my $c = \\$a;.

More succincly:

my $a; 
my $b = \$a; 

print $b; 
SCALAR(0x3e6c920)

my $c = \$b; 
print $c; 
REF(0x3e6c8f0)

print \\$a;;
REF(0x3e6c980)
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And:

my $a = 'fred'; 
my $b = \$a; 

print $b, ' ', $$b; 
SCALAR(0x3e6c980)   fred

my $c = \$b; 

print $c, ' ', $$c, ' ', $$$c;;
REF(0xf5e58)   SCALAR(0x3e6c980)   fred
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