The melakha of Dash involves separating the grain kernels from their stalks. This is generally done with the help of a tool or an animal (as explained in section 1). Thus, one who goes through husks by hand to separate the kernels has not transgressed a Torah prohibition, as he is not performing Dash in the usual fashion with a tool. However, the Sages forbid this because he is still separating the wheat kernels from the stalks. This is all on condition that he rubs the stalks off of the kernel with his hands, without a shinui. If he wishes to eat unprocessed wheat, he may rub the stalks with a shinui; for example, by using his fingertips rather than the palm of his hand.
The prohibition of Dash is not limited to grains. Rather, any action that separates food from its natural setting is a violation of Dash. Therefore, one may not remove legumes like peas or beans from their pods. Doing so in the way that it is done commercially for huge amounts of produce is a Torah prohibition, while doing this by hand is a rabbinic transgression. However, one may do this by hand with a shinui. If the pods are green and edible, then one may remove the legumes without a shinui, because the prohibition of Dash applies only when the shell is inedible (MB 319:21).
There is a tolada of Dash called Mefarek, which involves removing one thing from within another thing, and it constitutes a Torah prohibition as well. This includes squeezing grapes and olives (as will be explained below, 12:8) and milking an animal (as explained below, 20:4). Similarly, if one is interested in the liquid absorbed in a piece of clothing, one may not squeeze it out. The Rishonim disagree how egregious this action is. According to Rambam and Ramban, squeezing out clothing to extract the liquid absorbed in it is prohibited rabbinically, while according to Rabbeinu Tam and Rosh it is prohibited by Torah law (as explained in Harĥavot).
While a woman may nurse her child, it is prohibited by Torah law for her to express milk into a container because of the tolada of Mefarek (SA 328:34-35). If a woman’s breasts are engorged and she is suffering as a result, she may express milk in such a way that it goes to waste, either into the sink or into a vessel that contains something that will ruin the milk. This is because when the milk goes to waste, the prohibition involved is only rabbinic, and the Sages are lenient where pain is caused (SA 330:8). One may also attach an electric breast pump to a timer and then pump milk when the machine turns on (see below, 28:7).