Blood Sisters is the thirteenth episode of The Wild Thornberrys's first season which was first broadcast on October 27, 1998.
Eliza and Debbie get into a scaring contest, trying to out do each other. Eventually they, themselves wind up in the bat caves and a startling discovering.
The Thornberrys are near Kuzco, on their way to visit an old college Professor of Marianne's: Dr. Spinoza. The reason for their visit is because he is the world's foremost expert on the Vampire.....bat. Upon their arrival they find 'Dr. Spinoza' to be a hunchback whom acts a little weird. Spinoza leads them inside, where Eliza gets a bloody nose due to the change in altitude. She protests she is fine and flees to the Comvee. Marianne sends Debbie after her sister, which she does calling out in a creepy voice. Debbie finds Eliza once again reading her book about bats. Both girls agree that 'Dr. Spinoza' was very creepy. They then return to the castle, and get into a 'scare-off' of sorts.
The scare off ends with both girls winding up in the bat caves. When Eliza tries talking to the bats, she winds up scaring them, which in turn scares Debbie. They hear a moaning sound, and a figure approach, Debbie hears Eliza call out and goes to attack the figure when Eliza stops her and they find out the shocking discovery that man is reveal to be the real Dr. Spinoza is tied up by an hunchback imposter is actually the the village idiot had bought the satellite tv and watched to much horror movies for he learned from it.