When my bros and I were about 4, 6, & 8yo, we got together with Dad to make Mom a homemade birthday cake from the typical grocery store mixes. Back then even frosting was a mix, not a sweet glop you scoop out of a tub. We chose chocolate cake & white/vanilla frosting.
But, being 4 boys of varying ages but still in our silly phase, we had to improve it. So we food-colored the cake a very bilious green and the frosting was about grape-jelly purple.
Mom was … surprised. It took a LOT of food coloring to get the colors bright enough, and yes, we soon had interesting poop. And told all the neighbors all about our scientific triumph. No wonder they moved away.
We were sort of like Calvin, except there were 3 of us. How we survived to puberty is a mystery to all of us.