Leviticus 11:21
Yet these may ye eat of every flying creeping thing that goeth upon all four, which have legs above their feet, to leap withal upon the earth; Yet these may ye eat of every flying creeping thing that goeth upon all four, which have legs above their feet, to leap withal upon the earth;
The verse belongs to the law given through Moses that distinguished between clean foods that might be eaten and unclean foods forbidden to the Hebrews. It permits eating certain winged creeping things that go upon four, provided they have legs above their feet for leaping upon the earth. The distinction was not arbitrary but was given as a health and sanitary law to teach principles of health and to preserve bodily health and clearness of mental and bodily faculties for service.
Foods prohibited by that law, such as the flesh of swine and of certain other animals, were declared unfit because eating them fills and pollutes the blood with impurities and shortens life. Daniel and his companions refused the meats served at the king's table, including swine's flesh and other meats pronounced unclean, so they would not defile themselves. They chose instead food that would preserve their health and keep their minds clear for service.
Later teachers carried the restriction touching small flying creeping things beyond what God required, adding human food rules that burdened people with ceremonies. The extreme went so far as to require straining all water used, lest the smallest insect that might be classed with the unclean animals be swallowed. Insistence on such minor external observance while neglecting serious sins meets rebuke.