WHO GOES THERE?!

This Blue Jay was happily feeding on a suet cake, but kept looking over his shoulder occasionally, into the woods across the road from my place. He's stare for a moment each time, his crest raising then flattening then raising. Then he'd go back to eating. This happened four or five times. I couldn't see what was bothering him. Till about ten minutes later, when a big cat meandered through the yard from that direction!! It must have been lurking but the sharp eyed jay knew he was there!