On the reverse of '2 Kernteilchen mit Mutti' (two atomic elements with mum) Kippenberger stuck a newspaper clipping, which explains his interest in doing this work. The clipping reads: "The task of an atomic element of the pion (Pi-Meson) is reminiscent of a bird mother with two baby birds, who are already too big and whom she thus has to hold back from jumping out of the nest. The nest resembles the nucleus and the baby birds the protons. Protons are electrically charged and repel each other. Like the bird mother, the pion holds the nucleus together, jumping from one proton to the other. Scientists believe that the proton transforms into an electrically neutral neutron, but turns into a proton again as soon as the pion swings to another proton."