back odds

In a game of odds on, the first player will say "odds on you do x" to the second, implying they must give a number as odds to do a task x. Both players then say a number between 1 and the previously specified number. If the numbers are the same, the second player must do task x. However, if the second player says "back odds" after being presented with the initial challenge, the first player may instead end up doing task x. This happens if both of the numbers said add up to the odds given. This has lead to the crafty strategy of the second player asking for even odds with back odds, and saying the middle number. Therefore even if the first player were to say the same number, they would add to the odds, meaning the second player was safe and the first had to do the task, as back odds trumps the initial odds on. This is a legally binding contract and anyone failing to comply will be prosecuted in a court of law.

Player 1: Alright fella, odds on you shave off your eyebrow there.
Player 2: Ah mate that's kinda rough, ill do it back odds though.
1: Go on then ya cheeky cunt
2: 10 then.
*at the same time*: 3, 2, 1, 5
2: oh damn son you fool looks like your the one who's gonna be shaving his eyebrow today.
1: ah shit mate that was crafty, guess I'm gonna have to shave my eyebrow now seeing as how that we entered a legally binding contract and the numbers we chose both added to make the initial odds you gave me.