Your character has a small, pre-formed pond in the back yard. The pond is home to three goldfish and half a dozen frogs. Then there are a dozen frogs. The frog populations grows, till your character counts 27. A week later, there are fewer than 20, and a week after that, there are only 15 frogs, and a wet spot on the stones by the side of the pond.
Write a story accounting for the frog population. Nothing predictable. Stretch. Get into magical realism, sci fi, fantasy, even fairy tale or fable.