$ perl -MDevel::Peek -e'$x = 123; Dump $x; "$x"; Dump $x'
SV = IV(0x816a41c) at 0x814f69c
  REFCNT = 1
  FLAGS = (IOK,pIOK)                <-- Only contains an IV
  IV = 123
SV = PVIV(0x8150b10) at 0x814f69c
  REFCNT = 1
  FLAGS = (IOK,POK,pIOK,pPOK)       <-- Stringification has
  IV = 123                              been cached.
  PV = 0x81651a0 "123"\0
  CUR = 3
  LEN = 4