What is hidden behind the barrels?

A red shutoff valve is hidden at the lower-left pipe section.

What should I do with the valve?

Drag it onto the open lower-left pipe joint to close the line.

No. Move the barrels, reveal the red valve, and place the valve on the pipe.

Yes. The steam stops, Doctor Worry smiles, and the dialogue mentions hiding important things behind barrels.

Brain Test 4 level guide

medium 6 colors

Brain Test 4 Level 129 moves the barrels to reveal the hidden valve, then places that valve on the pipe to stop the leak.

If the player asks you to sign in, open the video on YouTube instead.

Press and hold the front gray barrel in front of the lower-left pipe.
Drag the barrel away until the red valve behind the barrels is visible.
If the second barrel still blocks the valve, move it aside as well.
Press and hold the exposed red valve and drag it onto the open lower-left pipe joint.
Release the valve in the joint and wait for the steam to disappear, the green check, and the completion dialogue.

Colors in this level:

Gray, Red, White, Brown, Black, Yellow

Trying to use the wrench or tape on the steam cloud; neither is the successful tool shown by the video.
Leaving a barrel over the hidden valve so it cannot be selected.
Dragging the valve beside the pipe instead of dropping it on the lower-left joint.
Stopping when the valve is visible but before the leak is sealed and the green check appears.

Board notes 5 details

Layout: Doctor Worry stands beside a gray pipe maze with steam escaping at the right; two large gray barrels block the lower-left section, while a wrench and a roll of tape sit on the floor.
Goal: Expose the hidden red valve behind the barrels and fit it onto the lower-left pipe so the steam leak stops.
Opening: Press and hold the foreground barrel covering the lower-left pipe area.
Danger Zone: The wrench and tape are decoys, and the steam cloud is not the draggable fix; clear the barrels before trying to use the hidden valve.
Mechanics: Moving the blocking barrels uncovers a red valve. Dragging that valve onto the exposed pipe joint closes the line and removes the steam.

What is hidden behind the barrels?
A red shutoff valve is hidden at the lower-left pipe section.
What should I do with the valve?
Drag it onto the open lower-left pipe joint to close the line.
Should I use the wrench or tape?
No. Move the barrels, reveal the red valve, and place the valve on the pipe.
Does the steam stop immediately after placing the valve?
Yes. The steam stops, Doctor Worry smiles, and the dialogue mentions hiding important things behind barrels.