Some people did not stutter before, but suddenly in one day (for example, at age 12) they start stuttering. How can research explain "sudden" onset of stuttering? My explanation is that this could involve a process known as *one-trial learning (or One-Time Learning)*, in which a single, highly emotional or threatening experience leads to the rapid formation (i.e., in a single event or experience) of an association between a specific stimulus and an involuntary defense response—such as freezing. This kind of learning is well-documented in fear conditioning and may help explain the sudden onset of stuttering in some individuals.