Some of the gore can be a little unsettling at times.
Gant's death was extremely bone-chilling.
Mark being beat up in the men's room. Completely unprovoked and unexpected and to make it worse, at one point, it seems to be over, only for for the attacker to strike again.
Carter's stabbing at the end of "Be Still My Heart". As he falls to the floor, he (and the audience) sees Lucy in even worse condition. That's right. As horrifying as the attack on Carter was, with only the aftermath, we instantly realize that whatever Lucy went through was even moreso.
There is a Season 8 episode with Abby alone in her bathrobe, when she hears a knock on the door, and she hears from the intercom that it's the pizza she ordered. She buzzes him in, and then opens the door to find out that it was the wife-hitter whose wife she had just saved. He tries to find out where his wife is, Abby doesn't tell him and he then leaves after a threat to call the police. She hears another knock on the door, and she stupidly unlocks the door (but leaves the chain lock on) and, it's still the hitter and he somehow forces himself inside and punches Abby until she falls unconscious.
There is an episode where Pratt is treating a 19 year old boy with a disorder making his bones incredibly brittle. Eventually he goes into arrest and Pratt attempts to put in a tube against the orders of Carter and the advice of Neela. As Carter enters what follows is horrifying. The pressure Pratt applies to the kids neck is to much and we are given a shot of the patients head leaning back slightly to far followed by a sickening snap, followed by silence as our cast realises that his neck is broken and the patient is now paralysed for life.
In "Two Ships", one patient, Adrian, comes in apparently in asystole, but Pratt and Ray performing CPR is keeping him conscious. Apparently, the nerves that control the heart were irreparably damaged. This is industrial-grade And I Must Scream. Pratt, Ray and Sam keep Adrian alive long enough for his family to arrive. Eventually, Adrian grasps Pratt's arm with a Single Tear, a sign that he's ready for Pratt to stop doing compressions on him.
The entire confrontation between Abby, Luka, and Curtis Ames, a patient with a stroke. Basically he proceeds to stalk Kovac for weeks, then proceeds to hold Abby almost hostage until Luka arrives, forces Luka to crush his hand in a vice, then kills himself on a rooftop. All while Abby is left wondering if he'll survive.
Pratt in the trauma room bleeding out of a carotid tear. Basically he's puking up blood.