What are the signs of someone huffing?

Depends: Huffing volatile chemicals (glue, paint, gasoline) leaves distinct odors on the breath and clothing, often stains around the mouth and nose. People who have been huffing act "drunk" - speech is slurred, coordination is impaired, balance is off and they may be disinhibited and even violent. Ether and nitrous huffing can cause death by suffocation, as can using plastic bags over ones head to huff.