Normally when holding onto egg yolks I've had to separate out while baking, I put them in a little glass with a small amount of olive oil or canola oil, to prevent them from losing moisture and to stop them from sticking to the glass.
The other day I had a little melted butter left over from the lemon-curd-blueberry tart I'd made. I figured I'd pour it around my two yolks in a small cup, stick the cup in the fridge and use the yolks in a day or so.
This morning I put the cup in the microwave because the butter had hardened in the cold of the fridge and I wanted to soften it up enough to get my yolks out.
Did I mention I hadn't had my required caffeine dose at this point?
My slowly waking mind was quickly reminded of an important physical concept as the higher moisture content in the egg yolks reacted more quickly to the microwaves than the lower moisture content of the butter surrounding them.
Expansive forces come into play where heat and moisture are concerned, and since the eggs were expanding faster than the butter was allowing them to... Faster than you can say "Kapow!" I'd received my little physics lesson... and decided that the microwave could definitely use a thorough cleaning.