Who Goes There?

Red Squirrel - I was watching the squirrel getting the nuts out of the feeder when suddenly something got its attention. It tried to stamp its foot on the feeder perch and got quite agitated. I took the pick when it was looking down at the ground in the wood. I don't know what it was that got its interest, it was'nt birds as it completely ignores them, and after a few moments it went back to feeding.