Tic
A tic is a sudden, repetitive, nonrhythmic motor movement or vocalization involving discrete muscle groups. Tics can be invisible to the observer, such as abdominal tensing or toe crunching. Common motor and phonic tics are, respectively, eye blinking and throat clearing.
Motorcycle accessories
A trailer hitch or tow hitch is a device mounted on a motorcycle that enables it to tow a motorcycle trailer. Legislation often restricts them to carrying baggage and not passengers.