On a pet forum people regularly talk about (and suggest to others) how they euthanize their old / sick rodents at home using carbon-dioxide unlike nitrogen like this capsule uses. I looked into what's the difference and it turns out inhaling pure carbon-dioxide instantly causes panic and the sense of suffocation and it's a horrible way to die. They were even able to cause an panic attack on a person physically uncapable of experiencing fear. There are videos online about killing pigs like this and it's not a pretty sight. Suffice to say I no longer take advice from those people.