DB<8> $a[0][0] = ['00', '01'];

  DB<9> $a[0][1] = ['10', '11'];

  DB<10> x splice @{$a[0]},0,1
0  ARRAY(0xb40000795febe168)
   0  00
   1  01
  DB<11> x @a
0  ARRAY(0xb40000795febbdf8)
   0  ARRAY(0xb40000795fee4240)
      0  10
      1  11
  DB<12>