https://wccftech.com/the-last-of-us-part-ii-features-dynamic-heartbeats-for-all-characters-will-hit-you-in-the-feels-for-killing-dogs/

The Last of Us Part II has quite a bit going on behind the scenes to make everything feel as immersive as possible. Naughty Dog recently confirmed every NPC has its own name, for instance, and fellow friends will use it in a desperate cry if they find his/her body.

Another cool aspect revealed by Co-Director Anthony Newman to Polygon is that every character, Ellie included, will have a dynamic heartbeat that controls their breathing.