Chess Opening Theory/1. e4/1...e5/2. Nf3/2...Nc6/3. Bb5/3...a6/4. Bxc6/4...dxc6/5. O-O/5...Bg4/6. h3

6. h3
This move looks natural, forcing Black's hand, but there is a surprising option for Black! /6...h5/ is a surprising move that forces White's hand instead.