$ perl -MDevel::Peek -e'my $x = 123; Dump($x); $x = "abc"; Dump($x);'
SV = IV(0x2764760) at 0x2764770
  REFCNT = 1
  FLAGS = (IOK,pIOK)
  IV = 123
SV = PVIV(0x2766c38) at 0x2764770
  REFCNT = 1
  FLAGS = (POK,IsCOW,pPOK)
  IV = 123
  PV = 0x27c1258 "abc"\0
  CUR = 3
  LEN = 10
  COW_REFCNT = 1

##</code><code>##

Head                   Body
+---------------+      +---------------+
| Ptr to body -------> | IV/UV slot    |
+---------------+      +---------------+
| Ref count     |
+---------------+
| Flags & type  |
+---------------+
| Unused        |
+---------------+

##</code><code>##

Head                   Body
+---------------+      +---------------+
| Ptr to body -------> | Unused        |
+---------------+      +---------------+
| Ref count     |      | Unused        |
+---------------+      +---------------+
| Flags & type  |      | Unused        |
+---------------+      +---------------+
| Unused        |      | Unused        |
+---------------+      +---------------+
                       | IV/UV slot    |
                       +---------------+

##</code><code>##

     + - - - - - - - +
     ¦ Unallocated   ¦ <--+
Head +---------------+    |
     | Ptr to body -------+
     +---------------+
     | Ref count     |
     +---------------+
     | Flags & type  |
     +---------------+
     | IV/UV slot    |
     +---------------+