Zero airspeed / zero rate of descent...all coming together at the same time and place! It tends to be 'positive arrival' compared to pussy footing about in the hover prior to touchdown. Take off: pull take off pwr and rotate immediately...in that order!!
Problems: If you don't know what the surface is like (depth etc) then because of the positive landing, there is a risk you may sink thru the light surface and damage the undercarriage. If you try and lighten the touchdown by pulling some power...you'll white out!
Take off: If you've been on the frozen deck for too long, you may stick to it sufficiently to overtemp an engine trying to break free!!
Fun and games....
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Thermal runaway.