What if a bear approaches you in the forest? What if you try talking to it, while backing away from it, facing it all the while, and it continues toward you? Unfortunately, the correct response may depend on familiarity that the bear has had with people. Has the bear learned to view people as sources of food or is the bear see you as being the food?
Some bears have become habituated to people, as people may have fed them in the past, of left food behind in campsites or picnic areas. This used to occur regularly in national parks, and still may be a problem wherever people and bears come together regularly. If you run into a habituated bear, it may exhibit a series of bluffs designed to scare you. The bear might stomp its feet loudly, or tear at the ground. It might huff or snort at you. You might hear a popping sound, or it may gnash its teeth together loudly and rapidly. It might even charge you, then stop short of actually making contact. These are not generally the actions of a predatory bear who intends to kill you. Most likely, this is a bear that may be frightened itself, and is trying to scare or to bluff you. In these circumstances, yelling might work, but only if the bear hasn't experienced this human response too many times before.
Should you play dead? That's what I learned in Boy Scouts many years ago, but many of the experts disagree, and they make some good points. Approximately 95% of bear attacks occur near campsites, picnic areas or garbage dumps, where the bears have come for food, and may now be feeling crowded or uncomfortable with your presence. Playing dead may not work because exaggerated aggressive behavior on the part of the bear is probably designed to scare you away from the food or to prompt you to get out of the bear's personal space. Lying down on the ground, playing dead, doesn't accomplish that. Also, you might consider that bears eat dead things on a regular basis. Some of the experts suggest that playing dead might only be effective if the bear sees you as a threat, as a mother with cubs might.