User blog:KennKong/What's eating my 5th pool column in Survival Endless?

In my current Survival Endless setup (sorry, no pic), I have (from right to left) three Gloom-shrooms, an Ice-melon and a Cattail. I regularly have to replace the Pumpkin around the Cattail, but I never see anything eating it! Do zombies surface that far back, can Snorkel Zombies swim under the other stuff, or can Dolphin Zombies jump that far?