Why would an otter save a stone?

Otters save stones primarily for practical reasons related to their daily survival.

• Tool Use: Otters are one of the few mammals that use tools. They often keep a favorite "pouch rock"—a stone tucked into a fold of loose skin under their forearm—to use as an anvil. They place the stone on their chest and bash shellfish or hard-shelled prey against it to crack them open.
• Efficiency: Finding a rock that is the perfect size, shape, and weight can be time-consuming. By keeping a "go-to" stone, an otter saves the energy and effort of hunting for a new tool every time they need to feed.
• Personal Preference: Otters have been observed to become quite attached to specific stones, often choosing ones that are smooth and comfortable to handle.

In short, it is a smart, energy-saving habit that makes their foraging much more efficient.