If a person takes the mother [bird] together with the chicks [which is forbidden by the Torah]: Rabbi Yehudah says he shall be lashed [for violating a negative commandment] and need not set the mother bird free. But the Sages say that he should set [the mother bird] free and not be lashed. This is the general rule: Any negative commandment which may be undone, does not render a person liable [for lashes].
Deuteronomy 22:6-7 states that it is forbidden to take from a bird’s nest both the eggs (or chicks) and the mother bird. If, however, a person did take both mother and children, and the mother bird was still alive, then he could undo his violation by setting the bird free. The alternative was to suffer the punishment for violating a biblical commandment: thirty-nine lashes (see Mishnah 3:10). Our Mishnah allows a person to “undo” the crime rather than suffer this severe beating.