DB<54> undef @x

  DB<55> x [ ($a=shift @x), ($b=splice @x,0,1) ]
0  ARRAY(0x34a6960)
   0  undef
   1  undef
  DB<56> @x=()

  DB<57> x [ ($a=shift @x), ($b=splice @x,0,1) ]
0  ARRAY(0x34a6f18)
   0  undef
   1  undef