My first decent bike as a kid was a Rayleigh Commando with SA 3 speed and the twist grip shifter.
I remember the "endearing" habit of those if they were not quite correctly adjusted - they could slip out of gear into a neutral between the gears, leaving you with no "drive". I was riding up the (moderate) hill to my house once, in top gear, standing on the pedals for extra torque, and the gear "let go" so I was suddenly standing on a pedal that was doing noting to resist me. I rather slumped forward and swerved into a parked car and fell off. A small amount of claret ensued!
(There was a lady sat in the car and the time who leapt out and to my assistance - and to be fair did not seem concerned about any damage to her car)