Rescue Me revolves around the lives of the men in a New York City firehouse, the crew of 62 Truck. Examining the fraternal nature and relationships of firefighters, the series tackles the daily drama of the life-and-death situations associated with being a firefighter, while exploring the ways the men use dark humor to protect their true emotions.
S1 e8 at 26 minutes. A dead monkey is sitting upright in the bathtub. S6e6 - at around 14 min in, fire truck runs over a cat and it shows the bloody and dead cat on the road.
Implied physical violence as well as depicted neglect and emotional abuse of one small child. As of this point in the show, also implied and referred to sexual violence against a minor.
It depends on your viewpoint. Tommy still gets to talk to his best friend anytime he wants, only he's now the friend is the main ghost in Tommys head after he burned to death during a rescue call.
S3e3 - approx. 34min in you see a horse who has some injuries but looks relatively healthy until he runs into traffic. It is not shown but you hear it out of shot.