Diana and Rosy and half of a peach each.

Rİddle: Diana and Rosy and half of a peach each. It was cut into half by the same knife but only Diana dies. How?

Answer: Because only one side of the knife had poison. So when they cut it one half of the peach had poison on it. She gave the poison side to Diana.

or

Only half of the knife was poisoned! Or perhaps, like in the original version of Snow White, only half of the peach was dipped in poison.