The blood that is counted as a liquid is the blood that flows from a kosher domesticated or undomesticated animal or fowl at the end of its slaughter. Blood that flows at the beginning of the slaughter, by contrast, does not make food susceptible to ritual impurity, because the animal is still alive. It resembles the blood of a wound or blood that is let.
When a person slaughters an animal and its blood sputters on to food, but that blood is cleaned between the slitting of one of the signs and the other, there is a doubt concerning the matter. Therefore the ruling is held in abeyance. The food is neither eaten, nor is it burnt.
A derivative of blood is blood let by a human being that was released with the intent of it being drunk. If, however, it was released as a medical treatment, it is pure and it does not make foods susceptible to impurity. Similarly, the blood released during the slaughter of non-kosher domesticated or undomesticated animal or fowl, the blood that is released with mucous or with feces, or the blood of boils, blisters, and blood concentrated in flesh, all neither contract impurity, nor make substances susceptible to impurity. Instead, they are like other fruit juices.
The blood of a crawling animal is like its flesh, it imparts impurity, but does not make foods susceptible to impurity. There are no entities analogous to it.