In cases of involuntary manslaughter by criminal negligence, a trial judge is not required to give a separate direction on the 'defence' of honest and reasonable mistake of fact because that defence is subsumed within the standard Nydam direction on gross negligence. A jury cannot be satisfied that conduct constituted a great falling short of the standard of care of a reasonable person without necessarily concluding that any relevant mistaken belief was unreasonable. The two concepts cannot co-exist.
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