Why is going pee refered to as #1 and poo #2 ?

Hey, maybe this seems like a silly question but I'm serious. Like ever since I was little my mom used the terms going number one and number two for going pee and poo. where did this originate from? cuz I know lot sof other people who call it that too. It make sno sense to me how you can derive a number from a... show more Hey, maybe this seems like a silly question but I'm serious. Like ever since I was little my mom used the terms going number one and number two for going pee and poo.
where did this originate from? cuz I know lot sof other people who call it that too.
It make sno sense to me how you can derive a number from a bodily function.
Thanks in advance.
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