Calvin was seen using a yo-yo at home once. He tried to make the yo-yo go back up, but it just stayed at the bottom. He shook his hand up and down, but the yo-yo stayed there. Because it stayed at the bottom, Calvin said, "I can't imagine mastering the skills involved here without a clearer understanding of who's going to be impressed."
In the last appearance of the yo-yo, Calvin claimed that he had a souvenir from the afterlife. He said he died of boredom while doing his math homework. He then said, "Eventually, my heart started again and I came back to life, but not before bringing this back!" The yo-yo never appeared again.