Old Tony (to Mark): "You said yourself that guitar needed tuning. So go ahead, boy, get tuning."
Mark (Johnny Crawford) sings "Greensleeves," a traditional English folk song.
The "quicksand" from which Tony and the McCains ultimately rescue Laurie is actually water filled with cork.
Karen Sue Trent is best known as "Penny Woods" on LEAVE IT TO BEAVER.
This is one of three or so episodes in which Mark (played by Johnny Crawford) sings.