I feel that there is something weird in this. In the struggle between Harry Potter and Riddle, Riddle can command the huge snake, but Harry Potter cannot (or rather, Harry Potter simply did not try to command it, but just kept running away). I wonder what's going on here? Does Harry Potter really not have this ability? But Harry Potter does have Parseltongue, and he can also command other snakes. But he took no action with this one. I wonder why the book was written this way? Could it be that the author herself couldn't make it consistent!