There is a technical difficulty: The vector field shown is a force-/ or acceleration field, but the animation pretends it is a velocity field. (Flow lines in  force field are generally NOT trajectories of particles…..). Nonetheless, the vector field analyzer provides exciting animation's even in these cases where a very cautious guided discussion is required -- but then again, the traditional static textbooks were even sloppier... Question: What does the reversed flow look like? Start with a square near the center, and see what its final shape will be.