Humans can mistake numbers simply by desire. If a person wants to win a prize on this game his/her mind will play the dirty trick to see -7<-8 simply because of the desire to win. This happens at subconscious level and it's the reason why store's prices are like $x.99. These prices are seen as $x not $x+1 just because we want to pay a lower price. This even happens to me, a math major.
When analysing these kind situations (where human behavior is involved) you have to consider human psychology or you can end up with wrong conclusions.

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