Yes. It becomes a dualvar-lite. Devel::Peek is very good at showing this.

>perl -MDevel::Peek -e"$_ = '20 ducks'; Dump($_); $_+0; Dump($_);"
SV = PV(0xd888c) at 0x2be2ff4
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0xd9acc "20 ducks"\0
  CUR = 8
  LEN = 12
SV = PVNV(0xda40c) at 0x2be2ff4
  REFCNT = 1
  FLAGS = (POK,pIOK,pNOK,pPOK)
  IV = 20
  NV = 20
  PV = 0xd9acc "20 ducks"\0
  CUR = 8
  LEN = 12
[download]

POK = has a string
IOK = has an signed int
NOK = has a floating point number
If there a "p" flag an no corresponding non-"p" flag, it's a generated value from numerical conversion or a temporary from magic.

See also: illguts.