RottieGirl, thanks for the link that describes predatory drift.
It provided a good description and explanation of why my normally good natured rottweiler mix, began to grab and shake a trespassing beagle who ran onto our property after visiting a neighbor. Fortunately Bella quickly responded to my husband's leave it command and the beagle was uninjured. I was not very pleased with the owners of that beagle, allowing it to run loose in a strange neighborhood and then driving off with their beagle standing up loose in the bed of their pickup truck
The majority of Bella's playmates are much smaller dogs and she's generally very tolerant of all sorts of rude behavior from small dogs. This incident was a reminder to us to continue to be vigilant in supervising her interactions with all dogs.