Subtlety was left to the human voice, which was, both for actor and playwright, the principal means of expression. Once again, this was a function of the space available. Although not much could be seen in the Greek theatre, everything could be heard. The acoustics of these theatres were excellent as, indeed, they still are. Epidauros, the best surviving example, is particularly famous in this respect. Every word spoken in the orchestra can be heard in the upper tiers. So can the striking ofa match, or a coin dropped on the central altar-base; these are tricks the tour guides regularly perform for visitors.