Paalus snuck near them, scouting them out. One of them snuck in a tree, probably seeing him. Paalus took out an arrow with a bag filled with a fluid on the front of it. Then he aimed almost straight up. With a steep arc, no one will detect him...he fired the arrow. Paalus flanked around.
The arrow began its descent, diving down into the camp. Once it landed, the bag splattered everywhere within a strong, burning substance. (Whether they dodge the fluid or not is up to you.)