It indicates that the person who sees the dream will help one of his loved ones to get rid of a slander, that he will show the truth to people by doing everything he can to reveal the slanderer and prove that the slander is not real.
To see that you are sucking venom from a snake in your dream means defeating a great enemy and achieving great success. To see that someone who has been bitten by a snake is sucking its poison denotes an important help to that person in real life, saving someone else's life and doing a great religious deed and receiving blessings.