[Steven Zahm]

@ Brittany

Ahhh, yes, sorry about that! The filter needs to return an array, not a string which is what $terms[0] would be. To help other who may come across this thread and do the same, here the corrected code:

add_filter( 'cn_search_terms', 'cn_exact_search_only' );

function cn_exact_search_only( $terms ) {
    return array( $terms[0] );
}