What's something that two conjoined twins would argue with each other about?

[TwistySisty]

I'm writing a story, and two of the characters are sisters who are siamese twins (or rather, conjoined twins, since that country is now Thailand). They basically share one body from the shoulders down. There's one scene where some other characters walk in on the two of them having a spat, but I'm not sure what a good subject would be for them to have an argument/fight over. Any ideas?

 

[Ben]

Nu uh i saw him first!

 

[Jaydox1]

whose turn to wipe?