Bikkurim, Chapter Two, Mishnah Seven
The mishnah compares the laws governing human blood with those governing the blood of beasts (domesticated animals) and the blood of a sheretz, a creepy crawly thing, which includes reptiles and amphibians.
1) The blood of those who walk on two [legs] is like the blood of beasts in that it renders seeds susceptible [to impurity].
2) And it is like the blood of a sheretz, in that one is not liable for eating it.
Section one: Interestingly, human beings are called those who walk on two legs (which invokes Orwellian images of pigs). In order for seeds (or anything that grows from the ground) to become susceptible to impurity, they must become wet by one of seven liquids, one of which is blood (see Terumot 11:2). The blood of human beings and beasts serves to render the seeds susceptible, but the blood of a sheretz (which is cold-blooded) does not.
Section two: While one is not allowed to eat the blood of a sheretz, one who does so is not liable for the biblical punishment of karet (if done intentionally) nor is he liable to bring a sin offering if done unwittingly. The same is true of human bloodit is prohibited, but one who eats it is not liable for either karet or a sacrifice.