The Rule of Three

ME: Mom, I want to get a picture of me, you, and grandma together.

MUM: Oh no, that's bad luck.

ME: What?

MUM: You can't have a photo with an odd number of people in it.

ME: Mom, that is completely ridiculous.

MUM: I didn't make up the saying. I'm just telling you what it is.

ME: So, I can't take a picture alone? You know one is an odd number.

MUM: ...

ME: What about an only child? Can't he take a picture with his parents? No family portraits?

MUM: Hmph! I told you, I don't make up the saying.

ME: Mom, just cos it's the saying doesn't mean you should believe it.

MUM: *Shrugs shoulders* I just saying.

ME: Hmph! I thought you didn't make up the saying.

MUM: *Tee-hee*