Causa sui (Latin pronunciation: [kawsa sʊi], American English phonetic: cow-SAH soo-EE) is a Latin phrase that means "cause of itself". As a philosophical concept central to Benedict Spinoza's thought, it denotes the only substance that has its reason for existing within itself, i.e. God.
While one may be tempted to refer to him in shorthand as "causa", that form is a gibberish fragment of a complete phrase, and he is giggling every time he sees it.