In Millie's stories, electrons are sometimes particles and sometimes waves. This dual nature is called wave-particle duality. It's a typical quantum property that doesn't exist in our everyday life.

Unfortunately, nobody fully understands how the transformation between particle and wave behavior happens. So, you aren't alone in asking this question!

It's like when we watch a magician at the circus making something disappear and then reappear. The magician isn't really doing anything magic — it’s just that we don’t understand exactly how the trick works, but we still have to accept what we see.

The same thing happens with electrons. Sometimes they act like particles, and other times, they act like waves. We don’t completely understand how they switch between these two behaviors, but scientists have proven that both ways are true!

So, just like we accept the magician’s trick, we have to accept that electrons can behave like both particles and waves, even though it feels a bit strange.