I got the slug mucus from a slug. I had a eureka moment when I rescued a slug from a puddle on the sidewalk during some rain and realized my hand felt slimier than ever. Slug mucus gets slimier when wet instead of rinsing off. So I put a slug in a little dish with some water so it wouldn't dry out and applied the slug where necessary when necessary along with some water. It ended up killing the slug after a few applications.
I'd do it again but I don't come across many slugs around here. It'd be real nice to have a dozen or so banana slugs around as pets. Maybe I should start a slug lubricant farm.
