gistfile1.php

<?php
/*
 * Plugin Name: Bleh
 * Description: Add bleh, blark or something to end of each sentence.
 * Author: Christian Axelsson
 * Version: 0.1
 */

function bleh_blehify_content( $content ) {
    $sentences = array_filter( explode( ".", $content ), "strlen" );
    return array_reduce( $sentences,  'bleh_make_bleh', "" );
}

function bleh_make_bleh( $result, $str ) {
    $blehs = array( "bleh", "blah", "blergh", "bloh", "blurf", "blesk", "blaf" );
    $bleh = $blehs[ rand( 0, count( $blehs ) - 1 ) ];

    return $result . "$str, $bleh.";
}

add_filter( 'the_content', 'bleh_blehify_content', 9 );

?>