Idiom of the week: Heads or tails?

You've used this expression a hundred times: heads or tails? It's what you say when you toss a coin in the air to resolve a dispute. 

We all know what a "head" is, but what about a "tail"? It's the rear part of an animal. Dogs usually wag their tails to convey happiness, and pigs have curly, funny tails. So, "heads or tails" brings two opposite parts of the body together, and by choosing one, you're rejecting the other. After that... It's all up to luck.

In Spanish, we have the expression "cara o cruz". The origin of our own version is a bit longer to tell. Maybe next week?