Most games wouldn't allow you to basically become an Indiana Jones villain, but Skyrim isn't most games - there are certain enemies you can kill by sneaking up behind them and RIPPING THE HEART OUT OF THEIR CHESTS. Sorry, Forsworn Briarhearts, but you got a rough deal in life.
The Forsworn are scattered about the Reach - hyper-aggressive tribal types who like to hang around hagravens. And most have a Briarheart as their leader, with the unfortunate weakness of being a semi-undead being whose normal heart has been replaced by a Briarheart. And if your Sneak skill is high enough, you can pickpocket their Briarheart right out of their chest, instantly killing them in a badass-yet-horrifying way.
Here's a weird thing - first off, there are mammoths who AREN'T tended to by giants. Second, you can distinguish the two by the tusks.
Regular mammoths have tusks that look like this:
...whereas owned mammoths have tusks with these markings on them:
So, now you know how to tell mammoths apart! Also, another way of telling if a mammoth is owned by a giant or not is whether there is a giant blasting you into the stratosphere at this exact moment.
Did you just kill a dragon and aren't sure where its skeletal remains are? The visual hint of "the enormous dragon skeleton that I just sucked a soul out of" not enough? Well, worry no more, because dragon remains actually show up on your map!
Get a map marker out to REALLY rub it in that you slaughtered a dragon by yelling at it.