Double Subjects 🟪 Do not use a pronoun immediately after the subject. The result is usually a double subject.
Snakes and lizards they are cold blooded.
(The pronoun they should be omitted.)
Snakes and lizards are cold blooded.
Pronoun-Antecedent Agreement 🟪 Make sure the pronouns in your sentences agree with their antecedents. (Antecedents are the words replaced by the pronouns. See page 475.)
The Marx Brothers launched his act in vaudeville before breaking into the movies.
(The pronoun his is singular. The antecedent Marx Brothers is plural.)