perl -MDevel::Peek -e '$n = "z"; Dump($n); $f = 3 + $n; Dump($n)'
SV = PV(0x804def8) at 0x8063ad0
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x805cce8 "z"\0
  CUR = 1
  LEN = 2
SV = PVNV(0x8080dc0) at 0x8063ad0
  REFCNT = 1
  FLAGS = (IOK,NOK,POK,pIOK,pNOK,pPOK)
  IV = 0
  NV = 0
  PV = 0x805cce8 "z"\0
  CUR = 1
  LEN = 2