They missed a real opportunity for "Omelette Doom Fromage" there

But yeah, I'd wager too subtle. I'm also questioning now how much rats use smell for navigating their environments. I notice that my cat is a lot more smell oriented than I initially thought and I think it makes a big difference. Hard to tell though.

Humans are /extremely/ visual compared to other animals: this tends to make us underestimate the intelligence of other animals (when we use visual intelligence as a proxy for general intelligence) and miss out on smart uses of other senses entirely. Rats are well-known for thwarting maze studies using things like fine sensitivity to slope, directional orientation using smell gradients across a room, or detecting the direction of researchers outside the maze based on micro-vibrations.

(Good book on the general topic of measuring animal intelligence: "Are We Smart Enough to Know How Smart Animals Are?" by Frans de Waal)