What showing must plaintiff make in order to amend the bill of particulars once the trial has begun?

The touchstones are excuse, lack of prejudice, and merit, according to the Second Department, in Cohen v. Ho, decided on March 20, 2007. Plaintiff's motion was denied because (1) plaintiff gave no excuse for the delay in seeking the amendment, and (2) defendant would be prejudiced since plaintiff was proposing a different theory of medical malpractice and, therefore, a theory of recovery which bore no resemblance to that recited in the complaint and the original bill of particulars. The court also noted that, in deciding such a motion, consideration should be given to the merit of the underlying amendment so as not to waste everybody's time.