There's funny things at play even beyond training effects, most likely. Even leaving aside that finding a dead person might be something that inherently triggers avoidance.

People screening luggage for bombs/knives/etc do significantly better if you show them a picture of a bad bag every now and then. Often these systems are used to monitor screener performance, but even if you just show them the picture now and then with "this is a test, no action is required" they do better.

Being primed with things relative to the task improves human performance, and I'd expect it would work in smarter animals, too.