Some cures not only didn't work, they could be dangerous to the patient. For instance, when someone was sick, doctors said that bad blood must be removed. To remove the bad blood, the doctor attached leeches to the patient (leeches are animals that suck blood). When the leech was full, the job was finished. But when somebody was sick, taking away their blood could make them very weak - they could even die. As science and medicine grew better, leeching was stopped until recently, when doctors began sometimes using leeches on patients who had fingers or hands that were cut off and reattached. One of the greatest pains in reattachment is just after surgery, when the blood pools under the skin and is very painful. Doctors have found out that using leeches to drink the excess blood helps to make the pain smaller.