Laura was making a jello mold for Christmas but forgot to buy mandarin oranges. She substituted fresh pineapple instead, not realizing that pineapple contains an enzyme called bromelain that prevents jello from setting. When she checked on the mold later, it was still liquid. Some online research revealed that bromelain degrades gelatin, the protein in jello. Canned pineapple can be used instead because its bromelain enzyme is deactivated during the canning process.