Counting Without Counting

You can instantly tell if there are three objects on a table, but if there are twenty, you would need to count them to be sure. Why can we spot the small groups without having to count, and how big does the group have to be for us to get out our mental abacus'? We find out in this Question of the Week, plus, we ask why should spit shine shoes so successfully? Like this podcast? Please help us by supporting the Naked Scientists