smell

the dogs made

the dogs made no immediate threatening moves.
But it was not safe to wait too long. A copter might arrive soon, and the humans had to be brought out of the plane before that. Presently four of the dogs, Clog, Blackeye, Brist, and Paddler, ambled nonchalantly to the plane's tail assembly, leaped up onto it, and then worked their way forward on the slippery metal to a spot directly over the passenger cabin. Glitter caught the sharp change in their smell as they prepared to vomit acid.
Inside, there was another flurry of near-panic as the humans heard the clatter of hard claws above their heads. Calm was restored shortly, however. The humans moved away from the area