This is easy to get while playing through the main story, but also very easy to miss. When you are returning some eggs to the big bird, you need to follow some Silent people to retrieve the eggs. One of them will lead you to a cave, in which they will be eaten by a bear. You would normally grab the egg and walk away, but stick around for this one.
If you sneak around to the bear's left while he's sitting in his little spot and go behind him and up to the ledge, you can find a pink berry. Press
Then, jump down from the ledge and walk past the bear to get its attention. Because of the berry, it will follow you. Go through the passageway that leads to a narrow bridge and make sure the bear is following you the whole way.
Keep going along until you get to the Silent Camp which you have to go through to get another egg.
If the bear is still following you, it'll start eating the Silent people and after it eats one you should get the achievement.
Here is also a video tutorial on how to get this achievement (not mine):