$s = '20 ducks';;
Dump $s;;
SV = PV(0x18aec0) at 0xa5b48
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x40cad18 "20 ducks"\0
  CUR = 8
  LEN = 16

##</code><code>##

$s += 1;;
Argument "20 ducks" isn't numeric in addition (+) at (eval 13) line 1, <STDIN> line 4.

Dump $s;;
SV = PVNV(0x40b1eb8) at 0xa5b48
  REFCNT = 1
  FLAGS = (NOK,pNOK)
  IV = 20
  NV = 21
  PV = 0x40cad18 "20 ducks"\0
  CUR = 8
  LEN = 16

##</code><code>##

print $s;;
21

Dump $s;;
SV = PVNV(0x40b1eb8) at 0xa5b48
  REFCNT = 1
  FLAGS = (NOK,POK,pNOK,pPOK)
  IV = 20
  NV = 21
  PV = 0x40d3068 "21"\0
  CUR = 2
  LEN = 40