I look after the neighbors' dog now and then, a 7 year old border collie. Every time we sit down by a stream or a lake, he'll go for a sip, startle at the sight of the dog under water, and start pouncing, digging and splashing like this. Or maybe he sees little fish. He'll keep at it until I distract him or he falls in, quite amusing
Also very good at pinpointing where the mice have built nests.
Which lead me to getting one of these.. probably the most over engineered mouse trap ever (electrocutes them).