Fridge: Doctor Who 2011 CS "The Doctor, the Widow and the Wardrobe"
Fridge Horror: What if the Doctor and Co. had shown up when the Doctor intended? They'd either be caught in the middle of the acid rain, or they'd be in the middle of a sea of battery acid, essentially.
Fridge Logic: Christmas trees, being pines, are monoecious, meaning that they have both "male" and "female" parts on the same tree. They're actually a terrible choice for a story which pulls the "mothers are strong" trope, since they're a "single gender" species. (It also makes the Doctor's talk about how motherhood is a fundamentally engrained part of life more obviously an example of Artistic License - Biology .)