It can most commonly be seen from the bottom of a hill, at the point where the slope meets the even keel of the ground. Looking up from here, especially when crouched, will reveal grass floating above the ground for no apparent reason.
Why Does This Happen?
This glitch occurs because the game will occasionally have issues reconciling the more subtle slopes in the game, and auto-generates grass where it thinks a hill should be, when in fact there is no hill there.
Effect on Gameplay
This glitch has no effect on gameplay, and thus likely won't be patched out anytime soon, as the appearance of some floating grass here and there is hardly an issue worth tasking a paid team of employees to fix. It is, however, pretty funny to see floating grass catch on fire with the aid of a molotov or a flamethrower.