Speech errors, or slips of the tongue, happen when speakers unintentionally deviate from what they want to say. Errors can involve word exchanges, such as “this spring has a seat in it” instead of “this seat has a spring in it,” moving parts of words while leaving others in place, as in saying “trucked two parks” instead of “parked two trucks,” or switching initial sounds in nearby words, as in “par cark” instead of “car park.” Despite being proficient talkers, all healthy adult native speakers occasionally make these errors. Slips occur not only in spontaneous speech but can also be induced experimentally, even without overt speech, indicating that they originate in the mind, not the mouth. Slips happen in all languages, spoken and signed. Errors provide insight into how humans encode thoughts into language when they speak, write, or sign.