While Dick attempts to draw a still life of an apple on the chalkboard, he places the apple on a book entitled "The Calculus." Sir Isaac Newton was the developer of calculus and, according to legend, was supposed to have been inspired to describe gravity when an apple fell on his head.
In an earlier episode, Harry says that his inner voice was speaking French, but that he doesn't understand French. In this episode, the entire family understands French. It seems that the aliens are supposed to be fluent in every language on the planet.