This is not an error of duplication. The full-fledged version of this Mitzvah are many and change for those who are learning the one/three chapter a day.
Positive Mitzvah 98
Impurity of Food and Drink
Leviticus 11:34 "Of all the food which may be eaten...and all drink that may be drunk"
Food and drink can become impure if they have come in contact with a source of impurity.