They can't. Amygdala is busted.
When you see something disgusting, be it a leech or a dead animal, the normal reaction of the brain is to tell you to STAY AWAY FROM THAT and match it with a gut reaction in the deepest part of the autonomic system.
If your brain doesn't do that then YOUR BRAIN IS NOT FUNCTIONING CORRECTLY AS-DESIGNED ACCORDING TO IT'S OWN TOPOLOGY. You need to take it back to the factory and exchange it for one that works properly.