According to My thinking

x[torch.tensor([[0],[1]])] == x[tensor([[0],[1]]) = x[[0,1]]=
tensor([[[1, 2]],
        [[3, 4]]])

This is because the torch considers the subscript as x[x-dimension][y-dim] which in our case is  x[[[0],[1]] which is still x-dimension with no y-dimension x[[0],[1]][No-y-dimension]

so it will return those values which are columns [1,2][3,4]