$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