What are some examples of observations or conclusions that would lead to you winning this bet? Likewise losing.

Good question. A candidate for deciding the bet would arise if:

Someone investigates some infant reflex in some species, that reappears in the adult under reproducible abnormal circumstances.

They physically locate the mechanism producing it in both cases and demonstrate it to be the mechanism, and the same mechanism in each case, not just a chance mimicry.

They examine that mechanism in the healthy adult.

Then I lose if it is present but having no effect, which might be demonstrated by excising it.

I win if it is found to be a functional part of the nervous system with an identifiable function.

Bet to be decided by the first such candidate that comes to the betters' attention.