Any person who shall knowingly sell or expose for sale the flesh of any animal which (a) was diseased or seriously injured at the time of slaughtering, (b) died a natural death or (c) may be found dead from a cause unknown to such person shall be guilty of a misdemeanor and, on conviction, shall be fined not less than five dollars nor more than one hundred dollars or imprisoned not less than ten nor more than thirty days; provided, that this section shall not apply to the sale of the flesh of any animal which is accidentally killed when the same is immediately prepared for market and the seller informs the buyer of the time, place and nature of the death of such animal.