When addition doesn't add up

Listened to an interesting programme about mathematics on the radio the other day.

Dr Eugenia Cheng discussed how 1+1 doesn't necessarily produce 2. Sometimes it is 1.

If you add one pile of flour to another pile of flour you still have one pile of flour.

It's all about context. When it is true and in what sense it is true.

Any ideas for other answers to 1+1?

https://www.bbc.co.uk/sounds/play/m001n1k5?partner=uk.co.bbc&origin=share-mobile