Chain Reaction is the fourth level of Vasebreaker in Plants vs. Zombies, Plants vs. Zombies: Journey to the West, Plants vs. Zombies: Great Wall Edition and Plants vs. Zombies: Great Wall Edition. This Vasebreaker level mainly focuses on Jack-in-the-Box Zombies.
Carefully break the vases to reveal Jack-in-the-Box Zombies, as they will destroy all the vases around them. Place Puff-shrooms where the zombies may end up and when possible, plant Hypno-shrooms next to a Football Zombie, not meeting any resistance. Be careful, however, as the wrong vase may result in a problematic chain reaction of multiple tougher zombies attacking at once. Make sure to be prepared in the event that this happens as it may be the main reason you will fail frequently and if you fail to hypnotize the Football Zombie, his high health will make him run through your defense easily.
- The level's name may implies about the fact that in this level, there are many Jack-in-the-Box Zombies, so once a Jack-in-the-Box Zombie is revealed, it explodes and breaks nearby vases, therefore more Jack-in-the-Box Zombies will show up and explode as well, resulting in more and more vases will be revealed.
- There is a sequel to this level called Another Chain Reaction.