Where a plaintiff establishes that an accident had some injurious effect on a pre-existing condition, the evidentiary onus shifts to the defendant under Watts v Rake to disentangle the accident from other potential causes; if the defendant fails to establish its alternative explanations to at least a prima facie level, the trial judge's causation finding will not be disturbed on appeal. The case also illustrates that competing inferences equally plausible to those drawn by the trial judge will not suffice for appellate intervention where the evidentiary onus has not been discharged.
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