I have a slug that I need to kidnap. Not an ordinary garden slug; this slug is special. This slug's slime is violently reactive with the atmosphere on my planet, and explodes into flame on contact with the air. The slug breathes oxygen, but doesn't need very much (or else it would suffocate). It also can be knocked out/made high on chemicals. This slug continually grows, with mature young ones being the size of a beaver and ancient ones being the size of a horse's body (excluding leg height). I'm aware this causes problems with the square-cube law, but we'll ignore that for now.
The slug's movement speed is quite slow, maybe about 5 meters an hour, and pouring water on the slime inhibits, but doesn't totally prevent, the reaction--even when totally submerged. Oil-based compounds do not react with the slime, although they can be started on fire by coming into contact with fire; if you could submerge the slime in oil totally without lighting the oil on fire, it wouldn't burn.
This slug lives in an old-growth forest where the trees are fire-resistant, but not fire-proof. Think something like a Jack Pine, where fire not only doesn't harm healthy trees, but is necessary for reproduction. The slug is followed by a trail of fire wherever it goes that burns out on its own relatively quickly (in general, think a day or two). Stones are available in this forest, but not in all locations.
I also have a hero or two who are considering capturing this slug and transporting it with them for at least a few miles. The problem is, they are in the middle of a forest with nothing but a staff, a knife, and a skin for water. They can make additional materials, such as a net, but they cannot bring any others with them from "civilization". How will they restrain and transport the slug while keeping it alive?
In the story heroes can unlock access to magic they can control with their thoughts, but these two heroes are not willing to unlock their access at this point; answers proposing they use this magic to carry the slug away will not be accepted. Additionally, it is OK to say they can't do it; I'm not committed to having it kidnapped just yet.
The whole story can be found at Story-go-round.