The second Zoe and Torby are alone in a room together, theoretically going to sleep, the giggling begins.
You open the door to check that they are still in their cots and silence decends. Innocent and sleepy faces look up at you. They seem to imply that they heard no giggling and you were imagining things.
Door closes and the giggling recommences.
Eventually they went to sleep last night.
This morning there was more giggling.
I went to check and only saw still asleep babies who blearily blinked at me and rolled over.