Eh, it's not quite as easy in this case. Since dango is served on a skewer, that means for an 'extra serving' you'd need to double what was brought out unless you wanted an argument over who would be getting the extra. And unless they were REALLY close sharing a skewer isn't something that would be done between two people, let alone the 5 Reimu was expecting here.
Hypothetically there may be some more back in the kitchen or wherever Reimu got them from in the first place, but it still means that what she brought to the table ended up being one portion short due to Koishi shenanigans.
