WordPress at a glance
action is not described

comment_duplicate_trigger action-hook . WP 3.0.0

Fires immediately after a duplicate comment is detected.

Usage

add_action( 'comment_duplicate_trigger', 'action_function_name_3925' );
function action_function_name_3925( $commentdata ){
	// action...
}
$commentdata(array)
Comment data.

Where the hook is called

wp_allow_comment()
wp-includes/comment.php 670
do_action( 'comment_duplicate_trigger', $commentdata );

Where the hook is used (in WP core)

Does not used.