Rats do better with a friend
Rats exploring a new environment do better with a buddy. Scientists measured rats second exploration of a novel space either alone or with another rat. Rats who had a buddy on that second trial were more exploratory, and the effect lasted through a third solo trial. Read more!
Rats do better with tickling
Jaak Panksepp's lab has long studied the ultrasonic "laughter" of rats, in response to play with conspecifics and with human tickling. Now it seems as though this tickling can have a lasting effect in improving rats' mood, and making aversive situations (such as injections) less disturbing. Read a nice summary of what we know about rat tickling here.
Token dog story! What is rolling over all about?
Dogs roll over a lot during interactions with other dogs. People often interpret this behavior is "submissive" so SCIENCE! tried to get a better understanding. @DogSpies does a nice summary of the study; turns out this subject got a bit complicated due to some bad media headlines misinterpreting the results as indicating that rolling over is actually AGGRESSIVE. Take home message: it's still about play! Read more here!