Most likely a grass goon spawned on top of you. If we had more time it'd probably be best to signal a warning right before a goon spawns, but as it is now as soon as a patch of grass reaches its max height it instantly becomes a grass goon. I'm not sure how noticeable it is, but we also have it so that the grass gets darker as it gets taller. I'm glad you enjoyed the game; hopefully this wasn't too frustrating!