Najafi Q&A: Slaughtering and Ritual Slaughtering

It is said that some non-edible animals can be properly slaughtered. What is the general criterion for these animals?

Does difficulty in slaughtering, which permits slaughtering, apply to the person attempting the slaughter, or to people in general? If a person cannot slaughter it but could seek help from neighbors or others, what is the ruling?

I live in Canada. As far as I know, animals here are slaughtered by striking the head of the animal with a device similar to a gun until it loses consciousness, and then the slaughter process takes place. The reason for this is to show kindness to the animal. This method, striking the head to render it unconscious before slaughter, does not lead to immediate death. Is it permissible to eat such meat? Is it considered halal, or is it similar to unlawfully slaughtered animal?

What is the ruling of the blood found in the rest of the carcass after slaughtering?