well, at the very least they are 'TRYING' to use somewhat of wit they possess... except continuously challenging anon for not allowing them to make koyukkuris. i say these yukkuris are a bit smarter than average wild yukkuris but not even close to pets...
I think I'm right in saying that neither one realizes they should stop and that Marisa was disappointed that there were no baby Marisas just like Reimu was disappointed in the last one that there weren't any baby Reimus.
Looks like they somehow tried to trick anon by putting Marisa's hat on Reimu. Anon could have done that, but it probably would have confused them if it wasn't their own doing.
The crack on the stalk made it doubtful that the koyukkuri would survive.(A moot point.) Now here is a question that I have not seen asked. How do yukkuri accessory's grow anyway?
Magic? They just do, leave it at that. I don't think anyone should try to explain it realistically. Have you seen what artists draw to explain how Reimu can move her braids? They draw her with arm-like appendages under the hair, which just makes her look like she's got dog ears. I don't think we should be trying to explain the hair either. A yukkuri's existence doesn't make sense, don't try to make sense of it.
The Reimu's appendages I could accept... But then I saw one with Marisa's "appendages"... (Three thin strands which are presumably braided...) That was taking it a bit far.