That was kind of a long drawn out experiment, but a lesson learned about linseed oil…. Never touch the stuff myself.
But stain rags and lacquer thinner rags all get hung up to dry.
Certain types of epoxy will heat up if left in a cup. I’ve seen them smoke before, but never spontaneously combust.
Another substance that creates a serious amount of heat when curing is super glue. I’ve cleaned up a spill with a rag and actually burned my fingers before. So be careful with that stuff too.