Swamped

It looks like another cauldron. You can't tell what's in it from here.

They don't seem to have a heat source, though. If that's the green concoction, then it shouldn't be active right now. They may be planning to use it wherever they're carrying it.

But it could also be something that produces fumes without being all that hot. Hard to say - it's not as if you're fully aware of this group's capabilities.

You opt to try to stay in the shadows. If they spot you, you can claim you had something especially sensitive to do and were trying to keep out of sight just in case. That should have some plausibility as a bluff.

You also make a point of watching where they're going, in case you find someone you can direct to follow them.

But you don't get very far in your sneaking efforts before you run into someone else skulking around in the same place.