From the Super Mario Wiki, the Mario encyclopedia
Vine-Triggered Platforms are devices found in Busted Bayou, a level from Donkey Kong Country: Tropical Freeze. They consist of a short vine attached to the underside of a hinged platform. Gripping the vine causes the platform, as well as any other nearby platforms, to drop down and become horizontal, possibly revealing items, such as bananas and Puzzle Pieces.
The platforms will stay horizontal for as long as the Kongs hold on to the corresponding vine. However, if the characters leave the vine, the platforms will return to their initial positions after a while. Vine-Triggered Platforms can be used to access possible hidden areas and items.
Before pulling a Vine-Triggered Platform, only the vine is visibly clear, the platform itself blending with the background. It becomes more visible once it is pulled down.