The bizarre-looking "clay figurine" they mention on p5 is called a 土偶 (doguu). There are thousands of these peculiar little things, mostly found in northern Honshu ("mainland" Japan) and dating from the early to mid first millennium BC. No one knows for sure what they were for, so as usual 'ritual purposes' is a safe bet. They mostly appear to be feminine, and many have those goggle-looking eyes. Some also seem to have been originally painted red.