I heard about similar episodes before, but now I witnessed it myself and it still seems pretty amazing. Here's the story:
I had a couple of hours at sunset and headed to one of my local spots for some dry fly action. White perch was getting ready to spawn and this is one of those times when you can catch a bunch of them on a dry fly. This is one of my little spring treats, a very relaxing type of fishing. They are easy to spot by the rises and put up a crazy fight once hooked.
Matching the hatch was not too hard, among the the tan caddis the mayflies were visibly targeted by fish and birds and soon the fish started to find their way to the net.
Yellow perch were in the mix too
And some chubs/fall fish
A minute after I released the last 13 inch fall fish, I spotted something silver moving on the bottom in front of me, in 6 feet of water. It started to get dark so I couldn't figure it out first, it looked like a half of a fish, but it was still moving. Then it got closer to me and I realized it was a fall fish, perhaps the one I had just released, in the process of being swallowed by a chain pickerel (essox niger). The things were not going in the right direction for either one of the fish. The fall fish was screwed, two thirds in the unforgiving jaws of the pickerel. But the pickerel's situation was not rose either. The pray was too big to swallow but also to big to spit out. Pickerel's teeth were doing too good of a job. Its gills were wide open but there was no water flow through them because the mouth was completely blocked. The predator and the pray were both heading for a slow death.
I stopped fishing and started watching the action. The pickerel was barely crawling on the bottom and the current slowly brought it closer and closer to me. I removed my net and once they got within my reach I tried to pick it up, despite the fact that I was in 4 feet deep water.
First attempt only lifted the struggling fish off the bottom a couple inches without even triggering the normal flight response. The second scoop was successful (not for my phone though, which needed a hair drier treatment and couples of days of rehab in a rice bag to return to function). I also got some water in my waders but it didn't matter.
Once in the net, the pickerel was able to wedge the fall fish out of it's mouth within seconds. I measured them: 24 inch pickerel trying to eat a 13 inch fall fish. More then half its length and wider too. Doable if you're a python or an anaconda. Not doable if you are a dumb greedy pickerel.