Here's a good clip of a couple male Hermann tortoises fighting. This is past the head-bobbing threat stage; it's full-blown combat. The bigger one appears to be bobbing his head, but actually, his throat pouch just rhythmically lifts the head when it expands to breath:
[video=youtube]http://www.youtube.com/watch?v=wYU-ilEZ7Gs[/video]
[video=youtube]http://www.youtube.com/watch?v=wYU-ilEZ7Gs[/video]