00:00 Leeches are making a comeback in some medical circles and are used for both medical and locomotive purposes, with land leeches having a tick-like behavior.

05:00 Leeches are blood suckers that can detect prey using CO2, and contrary to popular belief, they do not have 32 brains but rather two brains and 21 ganglia, with different leech species falling into three categories based on their diet: blood suckers, worm leeches, and jawed leeches.

10:00 Jawed leeches use their razor sharp teeth, called denticles, to create suction and saw deeper into the skin until they reach a blood vessel, while the giant Amazon leech, a jawless leech, uses a hypodermic needle to draw blood.

15:03 Leeches have a proboscis that they stick into your body to draw out blood, which is just as bad as the denticles sawing into your skin.

20:43 Leeches have simple eyes when they are young, but as they get older, they rely more on their ability to sense vibrations; their saliva contains compounds that thin the blood and prevent coagulation, making them effective at feeding and having potential medical properties; they can drink up to 10 times their body weight in blood and store it in a pouch with enzymes to keep it fresh; scientists are also studying the microbiota in leeches' stomachs to understand how they prevent the blood from spoiling.

25:35 Leeches have been found in various parts of the human body, including the nasal cavity, eyeballs, urethra, anus, and vagina, and can remain inside for weeks or even months causing discomfort and foreign body movement; there have been rare cases of leeches burrowing and moving around inside the body, such as a case in 1835 where a leech made its way from a girl's ankle to her thigh and had to be surgically removed.

30:36 Leeches reproduce by fertilizing each other's eggs and producing hardy cocoons, and some leech species, like the kangaroo leech, are doting parents that carry their young in a pouch until they are ready to fend for themselves; when removing a leech, it is important to be gentle and avoid squeezing or disturbing it to prevent infection.

35:42 Removing a leech requires breaking the seal it creates with its mouth and your skin, which can result in a wound that bleeds for up to 10 hours and needs to be cleaned and dressed multiple times.

40:51 Bloodletting, based on the humoral theory of health and disease, was a popular medical practice in the early 19th century, with leeches being used as a gentler alternative to cutting into veins, until it fell out of favor due to disastrous results and the rise of modern medicine.

46:22 Leech therapy has been used successfully to reattach body parts and improve blood flow by preventing blood from pooling and clotting, leading to the FDA approving leeches as a medical device in 2004.

51:29 Leech therapy is being used in the wellness community for various conditions, but the medical community is still unsure about its effectiveness and warns against overuse.