Georgetown researchers found that tobacco hornworm caterpillars could be trained to avoid particular odors delivered in association with a mild electric shock. (scientificamerican.com)
For example, a particular odor or sound, of no importance in itself, is taken by an animal as indicating the presence of another animal. (religion-online.org)
But each animal has to learn to associate a particular odor with a reward and then do something, like press a button, to let researchers know when they smell it. (discovermagazine.com)