Among other examples from “A Brief History of Time”Hawking has an extensive discussion in “A Brief History of Time”. Excerpt:
Two space dimensions do not seem to be enough to allow for the development of complicated beings like us (...) If a two-dimensional creature ate something it could not digest completely (...) because if there were a passage right through its body, it would divide the creature into two separate halves: our two-dimensional being would fall apart (Fig. 11.8).