Let's start with some definitions. "I-Spy" books were much loved by those of us who were kids in the 1970s - and probably by our parents too as they kept us vaguely occupied when on holiday. Each little booklet contained a list of things you might see (with a short, informative explanation), which you ticked off and got "points" for: in I-Spy Birds, for example, you got something like 5 points for a mallard but 50 for an osprey. You get the idea. Some were easier than others: the whole of I-Spy Churches could be completed on a single visit to York Minster, but I digress.
Once you'd amassed 1,500 points you could send off your book to Big Chief I-Spy at Wigwam-on-the-Green (why do I remember this stuff?) and it would come back with a stamp on it. Children were more easily pleased then.