Chicken Salad
Two toddlers, a boy and a girl, lived across the street from each other. Both dearly loved chicken salad. Each day, they took turns having lunch at his or her house and they always ate chicken salad. This continued until they were ready to start school.
The day before school started, their mothers found them crying. When asked why they were crying, they responded that they could no longer eat their chicken salad together. The mothers comforted them with the promise that they would pack their lunches and they could still eat chicken salad together every day.
The children did so every day. When they were about 11 years old, the girl unpacked her lunch one day and the boy, startled, said, "That's not chicken salad. You said you were going to eat chicken salad every day for the rest of your life. What IS that stuff?"
To which the girl replied, "This is peanut butter and jelly. I still love chicken salad, but I can't eat it anymore."