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 97
Impurity of Creeping Animals
Leviticus 11:29 "These also shall be unclean to you among the creatures that creep upon the earth"
There are eight types of creeping animals listed in the Torah. Contact with their dead bodies makes one impure.