Some things are being missed about grain... first, grain in film is RANDOM. It has no pattern and no consistent shape. Grain is different in EVERY FILM FRAME. What is more, the grain that makes each layer of color in the film frame has a different pattern for each color. This is critical to remember - grain doesn't form patterns you can see while a movie is playing because of these facts. When the frame changes, so does the grain pattern within the film frame (because the 3 colors' grain patterns also change for each frame) so you see a different pattern of grain 24 times per second in the movie theater. This makes grain hard for us to "see" in movie theaters unless the director really pumps up the grain to make it obvious. When the grain becomes obvious, images lose detail and become "noisy" - even blob-y
Anyway... "seeing" grain is very hard because of this. The director may use high quality film in bright daylight with normal exposure and processing for a grain-free very sharp image. If they shoot at night with reduced light and push the film via exposure and processing changes, grain will be much larger (and visible) in the dark scenes than it is in brightly lit scenes. In fact, the director may use different degrees of grain in various scenes as an artistic statement. Even when he COULD have a nearly grain-free image, he may choose to do something that introduces grain.
Can you see grain if you pause a Blu-Ray movie frame? Hmmmmm, not an easy question to answer. It would depend on the scene, the transfer, and whether the director did anything to make grain more obvious or less obvious.
Your TV may have more controls other than just Sharpness that will make slightly grainy movies look VERY grainy. It all depends on the set. It's always best to learn everything you can about what each of your TV's controls does so you can use it properly. Most Sharpness controls are set quite high by the manufacturer. Images will actually look better with Zero or very low amounts of sharpening (my display came with Sharpness set to "50" on a 0-100 scale, it looked crappy, using "10" makes images look MUCH better).
Anything you see in the movie that happens in blocks, even very small ones, if they have square sides and tops, that's a digital artifact of some sort. There are many types. Some come from transfer problems when film is scanned and converted to digital. Others come from processing the film images into frame data stored on the Disc in question. There are many choices for the frame data (i.e. 4.4.4 or 4.2.2, etc.). Grain is, if you will, an analog artifact that may be captured in high-def masters of movies originating on film.