Here's why:

* Two or more organisms: This indicates there's more than one species involved.

* One species lives on another: This suggests a close physical association, like one organism living on the body of another.

* Both benefit: This means both organisms gain something positive from the interaction.

Examples of Mutualism:

* Cleaner fish and larger fish: Cleaner fish eat parasites off larger fish, providing a cleaning service. The larger fish gets rid of parasites and the cleaner fish gets a meal.

* Bees and flowers: Bees pollinate flowers while getting nectar. The flower gets pollinated and the bee gets food.

* Oxpeckers and zebras: Oxpeckers eat ticks and other parasites off zebras. The zebra gets rid of pests, the oxpecker gets food.

Let me know if you'd like to explore other types of interactions between organisms!