Kernel-pult

The Kernel-pult is an offensive lobbed-shot plant for the roof levels. It launches either light-damage kernels or normal-damage butter which temporarily stall zombies (other than Dr. Zomboss, Zombonis and Pogo Zombies). Like other lobbed-shot plants, the Kernel-pult fires at a rate of 1/2x, meaning that the light or normal damage is an average of the damage of the kernels and butter.

Two Kernel-pults next to each other horizontally can be upgraded into a Cob Cannon.

Strategy
The Kernel-pult is best used in conjunction with other lobbed-shot plants, since it does not do a good amount of damage reliably. They are also good when used in conjunction with Spikeweeds or Spikerocks (not on the roof, of course) since if they stun the zombie while it is standing on the Spikeweed/Spikerock, it will take large amounts of damage from said Spikeweed/Spikerock.

This lobbed-shot plant is more useful than the Cabbage-pult overall, since it can stun, but if you want a better one, go for the Melon-pult. This plant is best used to increase the effective damage output of other plants; it slows the zombies, giving your plants more time to deal damage. At the beginning of a level, plant a Cabbage-pult and then two Kernel-pults; when two or three are used in a single row the zombies get buttered much more frequently.

It is especially important during roof levels as the incline of the roof will upset the firing of peas, spores, etc. It can also hit Screen Door Zombie and Ladder Zombies over their doors and ladders, and Snorkel Zombies while they're underwater (like all lobbed-shot plants).

It is best to use a combination of Cabbage-pults, Kernel-pults, then Melon-pults. It is a good idea to eventually replace Cabbage-pults with Melon-pults, and then with Winter Melons, however.

Trivia

 * An eyebrowless Kernel-pult can be seen in the Character Menu on the official Plants vs Zombies web sites.
 * In the iPod touch and iPhone versions of the game, there is also an image of an eyebrowless Kernel-pult for the seed packet. However, the actual Kernel-pult does have eyebrows.
 * A paralyzed zombie (a zombie with butter on its head) appears in the promotional music video Zombies on Your Lawn.