Single post hook

add_filter('the_content', 'our_modify_single_post_content');
function our_modify_single_post_content ($Content)
{
  //Exit if not a single blog post
  if (!is_single())
    return($Content);

  $Output = '';
  $Output .= '[Inserting at start]<br>';
  $Output .= $Content;
  $Output .= '[Inserting at end]';
  return $Output;
}