Size and Weight:
If you saw a picture of it without any sense of scale, you might find Compsognathus every bit as scary as its fellow theropod Tyrannosaurus Rex, with its sharp teeth, big eyes, and predatory stance--so you might be relieved to know that this dinosaur was no bigger than your average chicken. (See also 10 Facts About Compsognathus.)
Once thought to be the smallest of all dinosaurs, Compsognathus has since been bested by the even tinier Microraptor. But this dinosaur was not to be taken lightly: paleontologists believe it was very fast, with good stereo vision, and occasionally capable (perhaps) of taking down larger prey. As is the case with many small theropods, there's a strong possibility that Compsognathus hunted by night.
One controversy about Compsognathus that hasn't been settled yet is whether or not this early theropod had primitive feathers, like so many others of its breed. No trace of feathers has been found in existing fossils, but then again, a soft, downy coat would have left little or no imprint in the fossil record--and a feathered Compsognathus would fit in better with what we know about the small "dino-birds" that lived tens of millions of years later, during the Cretaceous period.