What happens when two dogs meet and greet one another?

According to Donaldson,

A good meet and greet consists of the two dogs making muzzle to muzzle contact followed by some mutual rear investigation. Then either play will break out or the dogs will go their separate ways. A male may urinate on the next available surface.

Dogs with polished social skills give many, many warnings that things are not going so well during a meet-and-greet, long before the situation gets to the point where there is a threat of injury to the dogs or people involved. Posturing, stiffness and standing over serve to give the other dog an opportunity to respond and offer and alternate bevahior.

Before dogs snarl or growl, you may observe a "volatile looking stance such as a stiff and growly T-position (perpendicular to each other with one dog's chin or chest over the other dog's withers)." Donaldson suggests that real problems can be averted by interrupting the encounter and disengaging the dogs with happy talk while separating the dogs from one another.