I actually taught this lesson this summer. I have also taught it in class several years ago when peanut butter was allowed in class (and the students were able to eat the results of their algorhythms). I substituted marshmellow cream for the peanut butter and used jellie and bread. You could substitute any food substance that had sticking ability...honey, almond butter, actual butter, etc. for the peanut butter. The substitution had no effect on the outcome. It is one of my favorite lessons!