Irresistible to the touch
If you ever had edamame you will know what a strangely pleasant action it is to squeeze out the pea. This infinite series toy replicates the sensation. The essence of this simple toy / keychain is irresistibility to the touch. Morinosuke Kawaguchi believes that the pleasure of touching needs to be integrated into product design.
Kawaguchi on the infinite series on his YouTube channel JapanTechLessons: