Final answer:
The most serious complication of performing a full hand scruff on a hamster is that the eyes can proptose, which can lead to significant injury.
Step-by-step explanation:
One potential complication of performing a full hand scruff on a hamster is that the eyes can proptose. Proptosis is a condition where the eyes bulge out from the eye sockets due to excessive pressure, which can occur when scruffing if not done properly or if the hamster struggles excessively. This is particularly important in species like hamsters that have large eyes in relation to their head size. It can result in serious injury or require surgical intervention to correct, so handling techniques should minimize stress and avoid excessive pressure on the neck and eye area. Other options, such as the hamster turning around and biting, the mouth not being examinable, or the hamster losing some fur, while possible, do not represent the most severe complication that can arise.