She looked surprised,
"What are you talking about?"
"If I win, then you have to do all my chores for the week." you say, surprising yourself with your sudden confidence.
She looked flustered, "No way! That's crazy."
"Then we don't play your game"
She considered this for a moment. Then a smile formed on her lips, and a very frightening one.
"Ok, but I get to change the game" she said quickly,
You raise an eyebrow
"I'm inviting my friends over later for a sleepover, to win, you must avoid all of our feet for the rest of the night until midnight, and if you win, I do your chores, but if I win-"
"Wait, no you can't change the game and add a bet."
"Yes I can, it's fair then. If I win, then we play until two hours after midnight."
"But what do you gain from that?
"During these two hours, you are not allowed to resist."
This seemed at first like an admittedly scary proposition, but you soon cleared your doubt. They are just little girls, what harm can they do? I bet they will just ask to end the game once they get bored.
You speak to your sister,"I agree-"
"Great! see you-"
"Wait, you didn't let me finish myself, I can change the game too, it's only fair.
She offered only a pout as resistance, but let you continue. This game had turned into something new and exciting. Your sister and you were always competitive, and now was the time to ultimately prove it.
"Well?" She said impatiently.
You actually cannot think of anything to add.
"okay, uh, I get a break in between the time of 10:00pm and 10:30pm you add, uncaring.
"Deal, you will loose by then anyway."
She ran off, probibly to call her friends.
You suddenly have an interesting idea. You could just leave the house when her friends get here, and win that way, they probibly won't know where you were, but if you do, then they will say you cheated, and want a rematch probibly. You don't know if you can handle many annoying kids trying to yell at you at once.