He was checking the outdoors for any stray aliens passing by and found himself nose to nose with a myopic young mourning dove.
He tried head-butting the glass, surely leaving him with a view of the galaxy and he made those funny throaty cat sounds, but his mission failed.
Little Mister Dove continued to gaze at his bird world without actually taking note of his adversary.
Go play with your toy mice Harry. You can win at that.