There are lots of 'humane' ways of killing animals that do not involve firearms (this is the illegal option given in the article).
Note that the author still tried an illegal method regardless (the BB gun, which is a projectile weapon).
> I had a brainwave. “I’m getting the blowtorch!” Brilliant! I could burn the possum.
I'd hope this was a poor attempt at humor, but given the actual methods attempted, who knows.
> I pathetically consulted my iPhone for ideas
If you need to consult your iPhone on how to humanely put down an animal, you probably shouldn't be doing it. Especially if you find some random advice about duck taping a knife to a broom handle and then follow it.
This whole article is horrifying.