Sam tried to stifle a cough as he knelt beside Frodo and offered him a sip of the brackish water he'd taken from the cistern on the edge of the road running east towards Mount Doom.  "Boromir was right.  The air here is a poisonous fume."

The ringbearer made a face at the taste of the water, but swallowed it anyway, his eyes red and swollen in his dirty face.

Sam blinked back tears and took his own drink, not bothering to hide his grimace.  He corked the water bottle and slung it back over his shoulder, and coughed again.  "What's odd, Mr. Frodo, is that I could swear I've smelled this before.  An' I don't see how I could've."

The cistern was long behind them, and the waterbottle gone along with his pack and pans, when he remembered.  

As the molten stone crept closer to the small hill upon which he and Frodo had taken refuge, the sulfurous fumes brought back a memory of watching in awe as a dragon made of light exploded into being over Hobbiton. When its broad wings had faded into ash, there was only a waft of brimstone-scented smoke to prove it ever existed.

A/N: A true double drabble inspired by the word "Fireworks" (and the fumes that were drifting into my bedroom window last night from the idiot neighbors, who were trying to rival in their own back yard a professional fireworks show).