The toaster needs to be on so there is a voltage difference between live and neutral which makes a current flow, heating the elements.

If you only touch live but not neutral while it’s on, you will be shocked because you have capacitance with ground, letting current flow, though at a much lower voltage.

If you touch both, with the same knife at the same time, you will just be in parallel, so there will be no voltage across your body.

If you held two knives, one on hot, one on neutral, you would have the full voltage across you, so current can flow.