Worst-case scenario: the UEd Goblin wipes the map and burns down your house.
Unrealed Default Texture
Have you ever wondered what that greenish bubbly texture in unrealed (Render.utx) is? It turns out to be a real life thing: Cave Pearls. As the name suggests, it's found in caves and it's made of calcite. The particular photograph it was based on originated from the so-called "Pearlsian Gulf" formation in the Lechuguilla cave complex in New Mexico.
The texture ended up being the default texture in unrealed prior do UE3. Most artists working on the original Unreal hated the texture and assumed it was a picture of bubbles. The fact that the "bubble texture" was generally disliked and stood out like a sore thumb on unfinished surfaces, was one of the reasons it became the default. It also was fairly white and uniform so it would show off lighting well in untextured levels. Before the original Unreal was released, the previous default texture was a light gray natural stone surface with some streaks in it. But since it was generic stone, level designers were more likely to forget to replace it on all the surfaces of the architecture they built.