use Devel::Peek;
@ary[1,100,500,1000] = ();
DumpArray(@ary);
__DATA__
....
Elt No. 998  0x4284
SV = NULL(0x0) at 0x4284
  REFCNT = 2147483634
  FLAGS = (READONLY)
Elt No. 999  0x106d0
SV = NULL(0x0) at 0x106d0
  REFCNT = 1
  FLAGS = ()