perl -MDevel::Peek -e 'Dump(%{$_[0]})'
SV = PVHV(0x157010280) at 0x15700ae40
  REFCNT = 1
  FLAGS = (SHAREKEYS)
  ARRAY = 0x0
  KEYS = 0
  FILL = 0
  MAX = 7

But what is this:

perl -MDevel::Peek -e 'Dump(%$_[0])'  
SV = NULL(0x0) at 0x100939eb8
  REFCNT = 2147483641
  FLAGS = (READONLY,PROTECT)

and this:

perl -MDevel::Peek -e 'Dump(%$^[0])'  
SV = IV(0x159825cf0) at 0x159825d00
  REFCNT = 1
  FLAGS = (PADTMP,IOK,pIOK)
  IV = 5796572328

perl -MDevel::Peek -e 'Dump(%{$^[0]})'
Number found where operator expected (Missing operator before "0"?)