>perl -MDevel::Peek -e"$_ = '20 ducks'; Dump($_); 0+$_; Dump($_); ''.$_; Dump($_);"
...
SV = PVNV(0x163a454) at 0x342be4
  REFCNT = 1
  FLAGS = (POK,pIOK,pNOK,pPOK)
  IV = 20
  NV = 20
  PV = 0x1639b14 "20 ducks"\0
  CUR = 8
  LEN = 12

##</code><code>##

>perl -wE"$_='20 ducks'; say 0+$_; say 0+$_; say ''.$_; say 0+$_;"
Argument "20 ducks" isn't numeric in addition (+) at -e line 1.
20
20
20 ducks
20