d'Armond Speers began speaking to his son only using a language made up in the Star Trek universe - Klingon.
While d'Armond was only speaking in Klingon, his wife was only speaking to their son in English. Speers says that he wanted to study how children developed language, and that he decided to use his son as a harmless experiment.
There are videos of d'Armond's son singing a Klingon lullaby, and even many notes scattered on the internet of the challenges that he faced while trying to teach his son Klingon! For example, there is no word for 'table' so instead he would just say 'thing which is flat'!
His son would rarely respond in Klingon, but when he did, his pronunciation was perfect and he never confused English words and Klingon words.
His son soon grew tired of his father speaking the fictional language and refused to answer him as long as he spoke it, so d'Armond decided to stop speaking to his son to avoid creating any problems in the house!
Today, his son speaks no Klingon, and d'Armond says that he isn't a Star Trek fanatic - he just really likes languages.