If unsure there is swelling behind the eye, look from above as well as head on but also you can attempt retropulsion and the bulging eye should not be pushed back. This can be diagnosed via looking in the mouth (recall close proximity of upper dental arcade to soft tissue floor of orbit) and/or identification of a fluid-filled cavity on ultrasound. If you are opening the mouth, ensure you do this under GA, these animals are in more pain when the mouth is open and hence they are very likely to bite you.