If you get a 2 for 1 unit train, suddenly your population is in the negative, and if you happen to also be low on food, you can neither buy a lodge or a farm (I forget the name of the most basic farm'esque food giving structure)
#2 for 1 bonus type puts you in a situation where you can't buy a lodge nor a farm
tawny jasper
smoky kite
You could take some villagers out of another building for a few minutes