Spatter

Imagine paint poured briskly down a channel with rough walls. Some of this paint will splash and leave
isolated blobs on the walls. The same thing can happen in lava tubes, and is most noticeable when the newer lava flow that barrels through an existing tube is a different color of lava than the existing passage walls. There has also been some speculation that spatter is especially likely to occur if the molten lava going through the tube hits some standing water and cools rapidly. The same processes that can form spatter may throw large enough blobs of material that they ooze down and form splash stalactites as well.