A teasing throttle is often found on air tools. It's a particular kind of throttle mechanism that allows the user to control the rotational speed of the tool precisely, for a gradual startup / run-down. I don't know what the actual mechanism looks like, but the "user interface" is usually a trigger, button, or lever, protruding from a handle, and operated by one or more fingers.
Several of these tools have "teasing triggers" (check the descriptions / pictures)
