The flight instructor in a multi-engine Diamond DA42NG reported that the pilot receiving instruction was on the controls, and reported feeling some fatigue and motion sickness due to light turbulence in the pattern at the airport in Palatka, Florida.
During their discussion they were distracted and did not complete the landing checklist and did not configure the airplane for landing. Subsequently, the airplane landed with the landing gear retracted.
The airplane sustained substantial damage to both engine gear boxes.
The flight instructor reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.
Probable Cause: The pilot receiving instruction’s failure to extend the landing gear and the flight instructor’s failure to verify that the landing gear was extended due to distraction, which resulted in a gear-up landing.
This July 2019 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

I want you (who ever you are) to pretend you are holding a yoke with your left hand, and trying to set power, or trim, or turn on pumps, or whatever. In the middle of that, do what you would do if you suddenly had to vomit.
What did you do with the yoke? Did you pull or push? Did you twist left or right? Or did you hold everything steady?
Try this in a sim holding the yoke, and see what your altitude does, and your heading, etc.
See why this situation is a PAN-PAN to Emergency in a flash? This is what that MEI should have been contemplating and taken over the flight right there. Otherwise that PAN-PAN could have become an emergency faster than you can react. Especially if it happened just as you crossed the threshold. .
Incredible lack of procedure from the CFI. We must not forget that the person in the left seat was a “pilot receiving instruction“
The CFI should have taken the controls. It was his fault.
I would not want that CFI as an instructor! He might as well be the ignorant student. There is no excuse for his lack of action. I would take his CFI license until he proved himself worthy if ever. Checklist Checklist Checklist! Really? What’s the sense in having an instructor if he can’t even do his job! Sad!
Air sickness can required cabin cleaning if the bags aren’t available.
The CFI was derelict.
At 100 AGL always verify 3 green or go around.