Yan Tan Tethera? A score? What do they mean? I'd make a terrible dodgy dealer: I've no clue how much a monkey, ton or pony is. But if you can speak sheep, you'll know what yan tan tethera and a score are!
A small number of sheep farmers still preserve the ancient way of counting sheep: 1-Yan, 2-Tan, 3-Tethera, 4-Methera, 5-Pimp, 6-Sethera...
When they got to 20 some shepherds transferred a pebble from one pocket to another to keep count before starting again. Others made a mark or 'score' on their crook to signify 20...