Yes, until you next use it in a string context.

There's no such terminating condition. 

>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

[download]

Another way to check is to count the number of numeric warnings: 

>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

[download]

In reply to Re^2: Question on SV internals by ikegami
in thread Question on SV internals by John M. Dlugosz

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