The most memorable 'nature' experience I've ever had involved a squirrel and a sparrow.

A squirrel was calmly and methodically foraging as squirrels tend to do. A sparrow landed nearby to do the same. They continued on their own for 10-20 seconds seemingly uninterested in each others presence until the squirrel ramped up from 0-100 instantly, viciously attacking the sparrow. I don't think the sparrow even had time to process what happened, there was no struggle from the sparrow.