Anne Hales familiar "brown Jenkins" is named after a character from hp lovecrafts dreams in the witch house where he is a also a witches familiar but a rat instead of a mouse
When Mercy is speaking to Isaac, she says "To everything there is a season, a time to every purpose..." and "a time to reap, a time to sow". These are lyrics from the song "Turn! Turn! Turn!" by The Byrds. She then says "The Season of the Witch", which is the name of a song by Donovan.