Sam is never aggressive towards people, even strangers, it's just for whatever reason if Dave is gone he becomes much more alert. Like cali~jenn said about Cutty almost like he feels the need to become the man of the house and protect us ladies (loki and I). Barks at things he wouldn't normally, gets out of bed at night and barks at things he hears, when if Dave is home he NEVER gets up out of bed at night. No matter what though even when Dave is home he always becomes alert and barks when someone knocks at the front door/rings the door bell, does exactly what @sheila says Butler does, barks very deeply and gets real stiff and stands real tall like a little soldier. Also like Butler does with Mario's kids, when Dave is being playful with me like comes up behind be and grabs and tickles me (I am super ticklish so I always let out some type of sound) or he picks me up Samson will jump on him until he lets me go. Like he thinks Dave is hurting me, he doesn't do this when we are being affectionate or anything just when being playful like that.