When a frog swims into a waterlogged fence, it will try to swim straight through. This locks the frog into a loop of trying to swim through the fence infinitely. The frog and tadpoles in the screenshot are "trapped" because of this but will pause every so often to glance at you.

If you try to lure them away with slimes they will not respond. You can remove the frogs from the fence with a lead, and their pathfinding will continue as normal, however.