Wet feet, also known as "airplane", is a movement technique that sets Jak to a grounded state while in mid air. This grounded state gives Jak a small frame window to perform a limited amount of other movement techniques as if he were standing on a normal ground surface. These movement techniques include combinations of jumping, punching, spin kicking, and zooming.
The technique is performed by first entering one body of liquid, and then, without moving below the original body of liquid vertically, moving above another body of liquid (including dark eco, lava, or water). Upon falling to the vertical coordinate of the first body of liquid, a standing state will be obtained for a short time, allowing the execution of other actions.
The technique is called wet feet because the setup requires Jak to enter a body of water for a moment. It is also referred to as airplane because it gives Jak a horizontal ground plane in the air that allows for more movement inputs.
The only known places that wet feet can occur are in Sandover Village utilizing the water fountain and in Lost Precursor City at the entrance to the puzzle room.
Large masses of liquids are typically composed of multiple segments of said liquid that act as one. Let's say there are 3 liquid segments. Segment 1 is placed right above Segment 2, and Segment 3 is right next to Segment 2. If Jak interacts with Segment 1, makes his way to Segment 3, and ends up on the same Y coordinate as Segment 1 while on top of Segment 3, he will experience 1 frame of grounded collision. As to why this happens, we currently do not know.
There is an instance of wet feet that commonly occurs in Lost Precursor City, but Bobbykaze was the first runner to discover that the technique was directly related to Jak interacting with water. After messing around with the water fountain in Sandover Village, Bobbykaze made his way over to the farmer's hut and encountered a mid air standpoint when roll jumping off a small ledge. He then reported the incident in the community discord server on June 24, 2020. Other speedrunners and glitch hunters soon began investigating the technique and where it could be applied in speedruns.