How to cull chick humanely?

I just wanted to say thanks for this thread and everyone who's replied. I sadly found myself in need of this information today. Being the custodian of animals is a big responsibility, and knowing how to help them die without pain is every bit as important as knowing how to help them live happy, healthy lives. So, thanks guys.

I am so glad I found this thread! Coup de Grass, I am so sorry you had to go through that with your chick! A month or so ago, I had to cull an adult guinea hen that my rooster had disemboweled. I felt like such a monster! I tried using pruning shears, but they didn't cut through her neck, so I did it three times to make sure her neck was broken. I felt so sick!
Now I have a pullet from an April order that I should have culled long ago. Her legs got splayed when she was a week old. I tried the piece of drinking straw/hair band splint, but it never helped. She was in the brooder with my other chicks, but I placed a bird cage over her and her food/water so the other chicks wouldn't step on her. They grew, she barely did. When it came time to move the normal chicks to an outdoor pen, I made a small brooder just for her in our front porch (out of the bottom half of a dog crate. She's very small for her age, but manages to use her wings to get to her food and water. Her legs are so heartbreaking! They are twisted and bent and one even appears to possibly be dislocated. She'll never progress and I wish I would have put her out of her misery a long time ago, but I kept hoping for a miracle or maybe just that she could be an indoor chicken. I know how wrong I've been, but couldn't bring myself to kill her.
Tomorrow I will end her suffering. I feel so sad that she couldn't have a normal chicken life. I am planning on the ether method, after what happened with my guinea I just can't try to snip her head off. Here are some pics of the poor little thing. I think she's a Sicilian Buttercup.

Sadly, but fortunately for me, my little pullet passed away on her own sometime this morning. I'm relieved that I didn't have to end her life and that she's no longer suffering.

I tried the ether method and was very unhappy with the results. Wondering others' experience with it and what I did wrong.

After our hatch I had two separate instances when I needed to euthanize. The first time I used a Ziploc and 2 well saturated wadded paper towels. The chick was in extreme distress for about 12 seconds and then quickly became unconscious and passed. I felt horrible about those 12 seconds - blubbering mess. The whole point was to be humane and it wasn't. I read some more threads to see if I did something wrong. Nothing obvious but the second time I added another paper towel, LOTs of fluid - there was extra in the bottom, and waited for 90 seconds to ensure the air was full of ether before putting the chick in. This time the chick was in distress for 5 seconds before unconsciousness but the point was to have it fall asleep with NO distress. Five seconds feels like a long time when something is screaming in panic.

Do most have those few seconds of panic cheeping or am I doing it wrong? Was not a good experience and I will be forcing myself to use the pruners next time.

I know this thread is old but thought I would add my way with a 4 day old gosling who couldn't absorb his yolk belly walk or even roll over eat or drink Goslings are stubborn and just dont give up. I took his heat away from him made comfortable Ice sacks wrapped in cloth so it wouldn't hurt him and he just went to sleep. when his core temp dropped he passed. It did take about a hour and I hated myself the hole time but didn't seem to suffer just sleep.