Here is a nice video of healthy dog to dog play. You can easily see all four parts of M.A.R.S. in this short clip of my Black and Tan Coonhound, Jolie playing with our young Welsh Springer Spaniel, Katie. M.A.R.S. stands for … 1. Metta signals. These are body language signals that say “Hey, I’m just playing … nothing serious going on here”. You can see how loose and wiggly waggly the dogs are. 2. Activity Shifts. You can see the dogs switching between wrestling, chasing, sniffing. 3. Roll Reversals. One dog is not also “On Top” They play evenly. And 4. Self Handicapping. Jolie, the larger Black and Tan Coonhound, makes herself smaller, gentler and plays at a level that does not intimidate or inure her smaller play companion.