Before judging, please read the description below (click Show More) after watching the video to fully understand what was happening and the predicament I was in.

I'm an inventive guy and I had an idea to build a squirrel proof bird feeder, but before I did that, I had to find out one thing about squirrels and that was what's the smallest hole they could go through to get to food. I searched google and found no information. I decided to do a small scale experiment on my own. There are about 10 squirrels in my neighbourhood which gave me a good group of volunteers. I love squirrels and I feed them daily and love watching them in my yard. Many people hate squirrels because they can be very destructive in attics and chew wiring which can be very costly and some make a sport of killing them for no reason. I have a few videos where I show how to catch them without harming them if relocation is an option. The only thing they have done is chew open many of my bird feeders hence the reason for building a squirrel proof bird feeder. I decided to place a large glass jar outside my living room window for them to go into to get a small snack. The jar opening starts out at 3" (7.5cm). I reduced the size of the opening by 1/4" (6mm) each day. I made sure each ring was sanded smooth, with no sharp edges, so the squirrels wouldn't be injured in any way. My thinking beforehand was.....they'd try to get in, and if they couldn't, they'd just leave. The jar was never left unattended. I video taped from inside the house.
The footage totally surprised me. They never give up.
Even though they struggled to get to the food, and had a hard time getting out, they kept coming back for more again and again for days. 12 days total of videoing.
At that one point, the squirrel was having a hard time getting out. I realized that if I unscrewed the lid, he would then be running around with a lid around its waist. That wasn't an option. If I tried to pull him out, it would most certainly bite off a large chunk of my finger. They have very powerful jaws and sharp teeth. After consideration, I knew that if it got in, it would get out. As you can see in the video, I was there to try to figure out what to do.I had to wait it out.
The squirrel proof bird feeder I made with the results works great and I still feed the squirrels daily.