With its boneless, wormy form, the leech appears to have no hard components at all, let alone a mouth full of teeth. So, are you surprised to learn it has three sets of teeth? In fact, leeches have a total of 300 tiny, razor-sharp, highly effective cutting instruments in those three sets [source: Šepitka]. Without all those teeth, leeches wouldn't be doing much bloodsucking at all.
Their method is almost surgical, which perhaps is why leeches are making a comeback in modern medicine; leeches are increasingly popular tools used in establishing blood flow to re-attached body parts [source: Lubrano]. When placed on someone's skin, the leech grabs on with its "mouth," which contains three separate jaws with 100 teeth each. Then, each of the jaws and teeth makes a separate incision, forming a cut (rather like a Mercedes-Benz symbol) that initiates blood flow, and the bloodsucking begins [source: Šepitka]. In between the teeth, there are ducts that release an anticoagulant to keep the blood flowing quickly [source: Šepitka].
Luckily for patients receiving leech treatment, those ducts also discharge an anesthetic, so the process doesn't hurt much [sources: Šepitka, Lubrano]. Unluckily for those patients, those ducts don't release anything for the eww factor.