The map TB Over Goo (also known as is Funnel Over Goo) the second map in the fourth chapter of Portal Stories: Mel. The map consists of two tests to solve.
After solving the second test, Virgil informs us that "test subjects rated this test as the hardest tests in this track. I've heard that it was made by two particularly cruel scientists.
A Weighted Companion Cube can be found in some debris at the start of the map. Attempting to pick it up will immediately fizzle it and give the achievement Forever Alone.
Hoopy the Hoop can be spotted in a secret room accessible by making a portal through a broken window. This is followed by Virgil, saying “people (are) obsessed with a silly hoop”.
The music played during this test is known as Troubled Water. A remix of Troubled Water was played in the trailers.
The second part of this chamber can be seen when entering a Chapter 4 map from the menu, focusing on a detached fluorescent light and zooming out over four shots, similar to Portal 2
