A Pentecostal believer in a spiritual experience may vocalize fluent, unintelligible utterances (glossolalia) or articulate a natural language previously unknown to them (xenoglossy). Commonly termed "speaking in tongues", this vocal phenomenon is believed by Pentecostals to include an endless variety of languages. According to Pentecostal theology, the language spoken (1) may be an unlearned human language, such as the Bible claims happened on the Day of Pentecost, or (2) it might be of heavenly (angelic) origin. In the first case, tongues could work as a sign by which witness is given to the unsaved. In the second case, tongues are used for praise and prayer when the mind is superseded and "the speaker in tongues speaks to God, speaks mysteries, and ... no one understands him".