Curious hawk story

I just received the following interesting story from my friend Mary:

[...] I also wanted to tell you a hawk siting, that maybe you will be interested in (or at least amused by). About a week ago, I was walking up the broken path to the Boulder Bridge (along the edge of the Midwood) when I noticed a Red-tail on the ground very close to the path. It was approaching some stuff on the ground, which turned out to be a tied up plastic bag of garbage, I guess. The hawk was inspecting the bag (this surprised me because I didn't know they were scavengers), and then it sort of jumped back, and I saw that the bag was stuck in one of its talons. Suddenly the hawk flew up across the path to a snag, with the bag dangling from its foot (it looked sort of amusing, but I was a bit concerned). Once it was up there, it was pulling something that actually looked like guts out of the bag. And it was also occasionally tugging at the plastic to free itself I suppose. I was getting late for work, so I decided I had to leave, and that the hawk would probably be ok. As I crossed the bridge I saw Peter over near the Tulip Tree nest with his clipboard [...]. I told him about the hawk, and my slight concern about it being stuck. But then I figured if a hawk can pull apart a squirrel, it can tear a plastic bag. I'm sorry but I really don't recall whether it was an adult (I had seen at least 4 Red-tails that day), and I don't recall exactly what day it was (but Peter might since it was his "inspection" day). So reading your blog hawk mystery, I thought this incident might be connected. Something could have been in the bag, I suppose, that was harmful/fatal.

Mary

According to "The Birder's Handbook" their diet is 85%+ rodents but "offal" is also listed. Offal is defined as "viscera and trimmings of a butchered animal often considered inedible by humans"...yum. I've never witnessed our local Red-tailed Hawks eating anything but live prey and I'm curious how he knew what was in the plastic bag.