Courtesy of List Universe:
1. A firefly is not a fly – it is a beetle
2. A prairie dog is not a dog – it is a rodent
3. India ink is not from India – it is from China and Egypt
4. A horned toad is not a toad – it is a lizard
5. A lead pencil does not contain lead – it contains graphite
6. A cucumber is not a vegetable – it is a fruit
7. A silkworm is not a worm – it is a caterpillar
8. A peanut is not a nut – it is a legume
9. A koala bear is not a bear – it is a marsupial
10. A sweetbread is not a bread – it is the pancreas from a calf