I only know of the jesus nut. What are the others?
lol "jesus nut" ... I like that.
Others include: Engine failure. Tail rotor failure. Control hydraulics/electrics failure. Imbalanced load (the smaller the bird, the easier this is for passengers to do mid-flight). Rotor damage (usually via flight into power lines or other hard-to-see but tough-as-nails material). Pilot error (discussed in an earlier post describing leaning forward too hard, leading to the rotor cutting something important, etc.).
The biggest issue with helicopters is the moment any single-point-of-failure pain point actually fails, the fucking things just drop out of the sky like rocks. Airplanes at least have aerodynamics allowing them to coast a significant distance if they're at high altitude when they experience a failure. A pilot operating a malfunctioning aircraft can sometimes have 10+ minutes of "steady, albeit aggressive, controlled descent" flight time to troubleshoot a problem and/or prepare for the rough landing. That's a
long time to figure out how to restart an engine, put out a fire, restore a busted control surface, start a backup system, reorient one's self (if lost), regain control, or at worst, select the "best" place to try to land and point the ailing craft towards it.
On a helicopter, if a malfunction occurs and it's a single point-of-failure element, you drop like a rock (or spin out of control with no hope of recovery). They're "neat" machines, in that it's neat they work at all, but they're risky as fuck.