R. v. Granada, 2013 ABCA 273 points out that expert evidence may be inadmissible but still not prejudicial. Generally expert evidence is excluded because it will be given too much weight and be prejudicial. But if the expert evidence is "unnecessary" (and so inadmissible) it may still be non-prejudicial if it merely states the obvious:
 Even if we were to accept the first argument, namely that the evidence was unnecessary and unhelpful, we fail to see any real prejudice arising from its admission. Simply put, if the expert's evidence was superfluous, in that it was testimony of the obvious, its admission may have been an unnecessary expenditure of trial time and perhaps even a distraction, but it did not extend beyond that. Certainly, it did not result in an unfair trial. To illustrate, the extent to which the trial judge relied on the expert's evidence is found in the following passage taken from his reasons at para 69:
There is the opinion of Dr. Ferber based on his observations of segments of the surveillance videos, that Ms. Granada was grasping a food product in her left hand and a small object in her right hand while at the merchandiser. There is the further opinion of Dr. Ferber that when she took her right hand away it was in a relaxed position, indicating that she was no longer holding an object in her right hand.
 In conclusion, we do not think the trial judge erred in admitting, or in accepting, the expert's evidence.