One of the central concepts in the Becca Fitzpatrick’s Hush, Hush series is that of Cheshvan, which according to Patch, is the only time a fallen angel can inhabit the body of a nephilim vassal.
What is Cheshvan? It’s a month in the Hebrew calendar that falls around October-November. It usually has 29 days, but no Jewish holy days. It’s name also signifies rain, since colder fall weather often brings rain, and in Jewish tradition, the flood of Noah began during Cheshvan. It is often also called Mar Cheshvan, “mar” meaning “bitter” because there are no holidays.
According to Jill Hammer of Tel Shemesh:
As the days grow colder, we enter the dreamtime of the year, seeking new meaning in our own inner depths. It is a time to write down our dreams, to explore our memories of our ancestors, to paint or write our stories–to go as deep as we can in finding our roots, so that we can prepare to grow.
It is also a time of paying attention to the body, which may explain why fallen angels are allegedly able to invade the body of another.