Tosefta sobre Chulin 6:12

One who slaughters for medicinal purposes, to feed to idol worshippers, [or] to feed to dogs is liable in covering up [the blood]. One who slaughters and renders [the animal] carrion through his actions, [and] one who [kills the animal by] stabbing or by ripping out [the throat], he is exempt from covering up. One who slaughters on the Sabbath or on Yom Kippur -- even though he is liable for the death penalty, as soon as it becomes dark [at the end of the Sabbath or Yom Kippur], he is [nonetheless] liable for covering if any of the blood remained. One who slaughters on a boat -- as soon as it arrives on dry land, he is liable for covering up if any of the blood remained, even though they said, "A person may not slaughter on a boat unless he has dust ready." One who slaughters and needs the blood [for another purpose] -- he should not slaughter in the normal way of slaughtering. Rather, how does he do it? He either stabs it [in the case of a wild animal] or he pinches its neck [in the case of a bird]. One who slaughters and dedicates the blood [to the Temple] -- he is liable to cover it up because the commandment of covering [the blood] takes precedence over dedication. One who slaughters and the earth swallows up [the blood without any act on his part], he is exempt, [but if] the wind covered it up, he is liable to to cover it up. One who slaughters is liable to cover the blood that is on the knife and the blood that is on the wings. Rabban Shimon ben Gamaliel says, since the blood was covered up by the sacrifice itself, he is exempt from covering it up. Rabbi Yehuda says in the name of Rabban Gamaliel, the slaughterer needs to make a blessing [on covering the blood] itself. [If] he slaughtered and did not cover it up, and someone else saw it, [the other person] is liable to cover it up. Even on Festivals one covers up the blood. We may cover it by hand but we may not cover it by foot, as a commandment should not be performed in a degraded manner. With what may we cover it and with what may we not cover it? We may not cover it with straw, nor with stubble, nor with clipped wool, nor with bones, nor with feathers, nor with wings of a dove, nor with the sawdust of carpenters, nor with beaten flax, nor with tree bark, nor with k'tzotzot, nor with [coarse] flour, nor with fine flour, and nor may he place straw on top of the blood and cover it. But it may be covered with limestone, with gypsum, and with earthenware that was crushed and made into dust. This is the general rule: Whatever is a type of dust, is absorbent, and [plants can] grow in it, we may cover up [blood] with it, and whatever [plants cannot] grow in, we may not cover up [blood] with it.