Zombies: The Hot New Grammar Secret Weapon

Thanks to a tweet from @johnsonr, who teaches the brave men and women of the USMC, we all have a foolproof and fun way to determine whether a sentence is in the passive voice:

If you can insert 'by zombies' after the verb, you have the passive voice.
 

Try it. It works.

• The concert was staged [by zombies] in the park instead of the auditorium.
• That test was given [by zombies] to juniors and seniors.
• Those lawns have already been raked [by zombies].
• Mistakes were made [by zombies] and lies were told [by zombies].