In the following game the computer was meandering its way toward victory, when suddenly it made an odd move, losing half a point. Machines don't blink, do they?
Wall, Bill - Bison engine
Palm Bay, FL, 2015
1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.Bxf7+
4...Kxf7 5.Nxe5+ Nxe5 6.Qh5+ Ke6 7.f4 d6
The "silicon" (i.e. popular with computers) or "annoying" defense.
8.fxe5 dxe5 9.Qh3+ Kf7
For Bill's experience with 9...Ke7 (which Stockfish 7, at 30 ply, sees as equivalent) see Wall,B - Redom,T, Chess.com, 2010 (1/2-1/2, 59), Wall,B - Qi,H, Chess.com, 2011 (1-0, 14), Wall,B - ubluk, Chess.com, 2012 (1-0, 35) and Wall, B - Guest3551214, 2013 (0-1, 35.)
About 1/2 pawn better than 10...Kf8 (in Stockfish 7's evaluation) as in Wall,B - Guest1839713, PlayChess.com, 2013, (1-0, 25).
11...Bd4 12.Rf1+ Nf6 13.Qf4 Rf8
13...Re8 was seen in Wall,B - Guest3789034, PlayChess.com, 2013, (0-1,35)
14.c3 Bb6 15.d4 Qe7 16.Qh4 Kg8
Black has castled-by-hand, leaving White with the insecure King. Although Bison has a piece for two pawns, Stockfish 7 sees it as only about 2/3 of a pawn ahead. Bill Wall is creeping up on the computer!
17.Bh6 Rf7 18.Nd2 Qe6 19.Rf4 Bd7 20.Nf3
20...Nh5 21.Rxf7 Qxf7 22.Ne5 Qe6 23.Nxd7 Qxd7 24.O-O-O Qf7
Bill tests the computer's willingness to pawn-grab, a traditional silicon weakness: 25...Qxa2?! 26.d5!? Re8 27.Qg4!? which looks unclear. The computer declines.
25...c6 26.g4 Ng7 27.b3 Rf8 28.Kb2 Bd8 29.Qh3 Be7 30.Qg2 g5
31.Rd2 a5 32.a4 Qe6 33.Bxg7 Kxg7 34.h3 Rf4
35. Rd3 Qf7 36.Qc2 h6 37.Rd2 Rf3 38.Rd3 Rxd3 39.Qxd3 Qf2+ 40.Kc1 Ba3+ 41.Kd1 Qg1+ 42.Ke2 Qh2+ 43.Kf1 Be7
44.Qe3 Qb2 45.c4 b6 46.Kg1 Qa2 47.Kh1 Qc2 48.Kg1 Bd8
49.e6 Qd1+ 50.Kf2 Be7 51.Qe5+ Bf6
This is not Black's best defense - in fact, it leads to an equal game - and it is not clear what the computer missed.
52.Qc7+ Kh8 53.Qc8+ Kh7 54.Qd7+ Bg7 55.c5
White riskily tries for more than the draw by repetition, which he could have forced the computer to find after 55.Kg2, especially after the dangerous 55...Qxb3 56.e7.
An accurate evaluation of the winning response 55...bxc5!? 56.dxc5 Qxd7 57.exd7 Bf6 was probably over both the computer's and the human's horizon.
Now the combatants cooperate to split the point.
56.Ke2 Qe4+ 57.Kd2 Qg2+ 58.Ke1 Qg3+ 59.Ke2 Qe5+ 60.Kd1 Qa1+ 61.Ke2 Qb2+ 62.Kf1 Qxb3 63.e7 Qxh3+ 64.Kf2 Qh2+ 65.Kf3 Qf4+ 66.Kg2 Qe4+ 67.Kf1 drawn