trained to drool on command.
"When you call my name, I'm Pavlov's Dog." Mick Jagger in The Bitch
In 1927, Ivan Pavlov experimented with his dog on the subject of psychological training--specifically conditional stimuli and response. He found that when he rang a bell each time before he fed his dog, the dog no longer salivated in response to the food, but to the bell.
A conditional response is when you're trained to respond to something such as Pavlov's bell, as opposed to using simply your reflexes.