Years ago, when I was still young and adventurous, I went on a ride at a state park called Free Fall <http://tinyurl.com/c6cjen9>. The concept is as it sounds. Riders are placed in a bucket and hoisted high in the air. Then the bucket is dropped and riders plunge straight down. It was a pretty scary ride.
I screamed as we dropped. But the drop was so long (because of the height), that I ran out of breath. So even though I was scared as I was falling, I wasn't making a sound.
My lack of screaming did not mean that I had stopped being scared. I had just run out of breath and could not longer make a noise.
When introducing our dogs to scary environments, we should be aware that they can indicate stress or discomfort in a number of ways. Just because a dog doesn't fight or scream or bark doesn't mean a dog is comfortable in the situation.
Some dogs might not complain because they are exhausted from fighting
Some dogs are naturally quiet even though they might be just as afraid as a noisy dog
Some dogs are frozen in fear
Some dogs have been punished in the past for barking or growling so they remain silent even though they are uncomfortable
Some dogs might be experiencing "learned helplessness"
They have learned that nothing they do gets them out of the scary situation, so they just deal with it. They have not learned to feel better; they have lost hope.
From Karen Pryor's "Don't Shoot The Dog":
"Psychologists have discovered in the laboratory a phenomenon called learned helplessness. If an animal is taught to avoid an aversive stimulus, such as an electric shock, by pressing a lever or moving to another part of the cage, and is then placed in a cage where there is absolutely no way it can avoid the shock, it will gradually give up trying. It will become completely malleable and passive, and may even lie there and accept punishment when the way to freedom is once again open."
Some dogs might even look playful or hyper when they are actually stressed:
From "Fired Up, Frantic, and Freaked Out: Training Crazy Dogs from Over the
Top to Under Control" by Laura VanArendonk Baugh:
"Even a hyper dog might not be enjoying himself as much as it appears. Frantic behavior often looks happy, with jumping and tail-wagging and licking, but in fact the dog may be just as stressed as the dog hiding under the table, only expressing it differently. While he may not be afraid, he is not in control of his own emotions and reactions, and that can be unpleasant"
From Nicole Wilde's "Help For Your Fearful Dog" :
" The involuntary instinctual reaction to fight or flee in the face of danger is known as the 'fight or flight' response... There are two other responses dogs may display when confronted with danger. The first is simply to freeze in place...The second is known as 'fidget/fool around'. A dog may search around on the ground or perform other canine equivalents of human fidgeting, or bounce or wiggle about, acting in a way we would term silly... Dogs may go into to fidget/fool around mode when trying to get
another dog or person to stop acting in a threatening manner.
So when our dogs are placed in high intensity situations - like dog parks, and day care, we need to really assess if the dog is actually having a good time or is actually stressed.
Read more about stress indicators here: http://blog.mysanantonio.com/latrenda/2011/03/denver-the-guilty-dog/
and here: http://blog.mysanantonio.com/latrenda/2013/04/possums-are-not-the-only-animals-who-play-possum/