Playful actions to watch for:
  Back and forth play – dogs change position – role reversals
  Bouncy, exaggerated gestures
  Wiggly bodies
  Open relaxed mouth
  Play-bows
  Twisted leaps or jumps
  Pawing the air

Signs of Anxiety/Stress to Monitor:
  Fast wagging low tail
  Whining or whimpering
  Ears may be back
  Hiding behind objects or people

Signs of Fear:
  Dog will try to look small
  Tail tucked
  Hunched over, head down
  Tense
  May urinate submissively

Red Flags that Require Intervention:
  Excessive mounting
  Pinning (holding another dog down and standing stiffly over them)
  Shadowing another dog (following) incessantly
  Bullying: repeatedly bothering another dog that does not want to interact
  Fast non-stop running with a group – high arousal situation
  Full-speed body slams
  Putting head repeatedly onto another dog’s neck or back
  Staring with a fixed gaze directly at another dog
  Snarling or raised lips
  Showing teeth
  Hackles up at the shoulders
                                *Association of Professional Dog Trainers, apdt.com