Ctrl-F for "2D" (2-dimensional creatures), although I can't find the "discovery", maybe I remember it wrong.

Btw, this was one of the mindfucks I learned studying physics. Other ones are:

  - dimensional analysis: checking if formulas can be wrong, and more importantly, finding formulas (eg, period of a pendulum) just by analyzing units that can be involved (no constants obv)  
  - similarly, rate of growths in dimensions: why giants can't exist (bone resistance is proportional to section area and load (weight) is proportional to volume  
  - Conservation laws derive easily from symmetries (energy from invariance in time, momentum from invariance in direction etc)