Who saw that? Well, the POV character, presumably. Or the omniscient narrator, but you've set that up, up front.
So then these sneaky little terms keep showing up: "he saw", "she felt", "she heard".
Except that sometimes you've got to use them.
For one thing, they establish POV, which helps. Free-floating thoughts and impressions can make the story very silly in short order.
They loosen up the POV, which is sometimes what you want, to make it clear that while what is said is what is sensed or thought by the character, the language is not exactly as used.
And if the character is observing for a long time -- awkward, but sometimes necessary, as when the character is perched on a rooftop and watching a mob tear apart Lord Broadacres's fancy house, and none of the rioters have the necessary perspective and they aren't POV characters anyway -- sometimes you have to throw them in to remind the reader of the character's very existence. Reactions help, too, but sometimes the character is too focused on the event to notice his own reactions.
And sometimes because the noticing is the chief action. Particularly to report events out of order. "The jug fell over. The water sloshed about Jack's feet." is the real order, but if Jack doesn't notice it until the water hits, "Water sloshed about Jack's feet. He looked over and saw the jug had fallen over." Or that a detail got missed. Describe the room, and then highlight the blood on the floor by having Jill see it. . . .
It can be an interesting juggle.