Pat Gorman in a role c1960s
You've probably seen TV extra Pat Gorman more than any other actor, without even knowing

Extras – or supporting artists, to give them their official professional title – are the unsung heroes of television. Herded about like cattle, paid a pittance, but without them nothing would look quite right.

Strict union rules govern the employment of extras. They can move all together in a crowd, but if one extra is required to act in an individual, specific way, they go up a pay grade. If they are required to say something – they can utter 13 words or fewer – they get another threepence. Those words, however, cannot be specifically scripted. This is a halfway house between "rhubarb rhubarb" and actually acting. It's the difference between a script that reads: "The man shakes his angry fist and calls after the thief", and one that reads: "The man shakes his angry fist. Man: Oi, come back here, you scoundrel, I'll tear you limb from limb, I'll thrash you to within an inch of your life, you see if I don't". The latter is acting, and requires a professional in the field.