Which formal fallacy is committed in the following argument: If your pet is a cat, then it has a tail. Your pet is not a cat. Therefore, your pet does not have a tail.

The argument denies the if-clause and then denies the then-clause, which is invalid.

The conditional says being a cat is a sufficient condition for having a tail.

A sufficient condition can be met in other ways, so a tail may exist without the pet being a cat.

From not-a-cat nothing follows about the tail, so the negative conclusion is unwarranted.

Negating the antecedent to negate the consequent is the fallacy of denying the antecedent.