The operator applied the fleam to the vein previously swollen using compression. The fleam should be held gently, as if it were a feather. Then the practitioner struck the back of the blade with a long wooden mallet such that the skin and the wall of the vein were pierced at the same time. Removing the blade opened the gap and caused the bleeding. When the practitioner considered that enough blood had been drained, he closed the edges of the incision with a pin, tore a few hairs he soaked with blood or saliva to bind them in a "figure-eight" to retain the closure. The animal was kept still for a few hours after the operation. The pin was removed six to eight days later.
Bloodletting was not without risk. The fleam could hit the trachea or the common carotid artery, resulting in the formation of a large hematoma. Phlebitis and thrombosis were common. Finally, blood loss could hasten the patient's death.