Rick Walking Dead and zombies against passive voice
When the subject is acted upon by the verb, this is called 'passive voice'.

Not sure how to identify passive voice? Here's a good rule of thumb: If you can add “by zombies” after a verb - it’s passive voice.

Example Fix
The house was haunted [by zombies] The haunted house
The game was released [by zombies] last week Nintendo released the game last week

This article goes into more detail on how to use the "zombie test" to improve the readability of your article.