Any bird can appear like a swan by painting its beak and feather. But what will happen when the time for separating water from milk comes?
When a crooked person appears simple to you don't get carried away. Even the most poisonous snake who always make zig zag movements becomes straight while entering into the hole.
A bad person remains mean even after living in the company of good persons. A snake living on the trees of sandalwood remains poisonous.
A person who does good during his life also does good at the time of his death. A person who does evil during his life also does evil at the time of his death. Jatayu and Marich can be considered as examples of this.
Look at the cotton in the bed and the iron in the stone cutting tool. Both the cotton and the iron are being hurt, cotton for the benefit of others and iron for hurting others. Good persons are like cotton and wicked ones like iron.