Rather than taking the course of Gordon Dickson's first contact novels, where races are sociologically different, and must be interpreted, the Thranx and humans deal instead with reactions over each other's bodies.
The humans react, at first, very poorly to the Thranx, not only because they are alien, but also because they look like giant bugs, and they must fight a seemingly innate human fear of creepy crawly things.
The Thranx find themselves at odds with the humans firstly out of a belief that they are the only intelligent organisms in the universe, and secondly out of an innate primal fear of mammals, since those that exist on their homeworld are fairly vicious and barbaric.
There are also issues of climate to deal with, the humans being used to much cooler, dryer climates, whereas the Thranx, being cold blooded, much prefer hot, wet climes.
Using physical differences still works very well in the book...perhaps one of the better moments of the book comes when the humans bring a small child to encounter a thranx child, and the human tries to play a game of cowboys and indians (where the cowboys are landstealing murderers, and the indians are peaceful indigenous heros) and neither, of course, wants to be the cowboy...Many reflections are made on differences encountered on very shallow differences. The book, as with many Foster novels, is perhaps a bit heavy in it's moralization, but still very entertaining.