Hemiola

How can I explain a hemiola to someone who knows nothing about music?
A hemiola is suddenly going to half speed when the normal rhythm (which can even continue in other instruments at the same time) has an odd number of ...
Is that a hemiola or what?
What is the difference between syncopation and hemiola?Is a hemiola a polyrhythm?What is the hemiola in music?What is the difference between syncopati...