Henry finds himself in need of a pointy object. If you don't want to bother with getting the Pointy Knife, you can get the Desert Thorn instead.
Go into the plant shop, marked Store, to the left of the Settlement. Use the space bar to see hotspots, if you need to.
The Fruit Fly is a bad guy. He murders his plants. Perhaps that's justification for violent action. If not, you can get a pointy object another way.
OK. I have to warn you, I can solve it but I'm not entirely sure I understand how this puzzle works and may not be able to explain it very well. Start by exploring everything in the shop.
The Lever opens the Skylight. The Left Button (green) and Right Button (red) move the Claw left and right. The Red Lever makes the Glowy-Blossumbutts, um, extend a pink flowery bit for a short while? (I'm no botanist.) The Cycle Button (which unlocks during the puzzle) turns the Plant Food into a Hive. The Stink Plant (whose hotspot is only available when the Skylight is closed) releases stink when you touch it. The Giant Flytrap forms a part of this too.
It's difficult to know what order to provide them to you, but ... Have you tried putting the Plant Food (on the Claw) under the sunlight? It will become glowy for a bit.
Have you noticed the scary Giant Flytrap? It's currently asleep.
Perhaps it would like some glowy Plant Food? Or perhaps the glowy Plant Food dazzles it? I'm not sure. Either way, try taking the glowy Plant Food close to the Giant Flytrap.
Talk with it. It is afraid of the Fruit Fly. Also, it presumably eats flies. Also. Where its dialogue says, "Help me to help you," you can skip the rest of the puzzle entirely, if you like.
Try taking glowy Plant Food to the Glowy-Blossombutts when its pink flowery thing is extended. (Pull the Red Lever.) This has to be done quickly beacuse both the glowy Plant Food and pink flowery extension are timed events.
If you have done this correctly, the Grizzly-Grumpuphigus will blow air.
I think the aim of the puzzle is to get the Giant Flytrap to move to the left, so it can eat the Fruit Fly. It is attracted by the Hive's insects. Manipulate all of the abovementioned puzzle pieces to entice the Giant Flytrap to the left.
Use these steps when the Giant Flytrap is to the far right, in the original position, but awake.
Then, use these steps when the Giant Flytrap is in the middle position.
This time, the Giant Flytrap will go to the left and eat the Fruit Fly.
And, you know what? Explaining this to you made me understand the puzzle much better. I solved it by accident, the first time.
The Fruit Fly can't stop you any more. Take the Pointy Knife.