The photo above showsa radial cross-section of the log, as revealed by a hammer and some wedges. You can see the knot, which ends abruptly. You can see several years' growth were curved as they wrapped around the cut end of the branch. But you can also see that towards the bark side of the cross section (late in the tree's life), the grain is straight as you can ask for above the knot.
This closeup shows how straight the sawcut was that cut off the branch. What's amazing to me is how clearly you can still see the sawn end of what was a branch. It looks like within a few years, the cut was healed over. I should state here that there was no indication on the bark that a knot was in here.
Another woodworking truism is illustrated here: every branch, and therefore every knot, begins at the pith. Knowing that can help you visualize where a knot might travel to (and not) in a board. Also notice that the branch grew at an upward angle. This is more prevalent in hardwoods like this oak; knots in conifers like pine, spruce, or tamarack tend to be closer to horizontal. (In both photos, the lower [stump] end is on the left and the upper [leaf] end is on the right.)
So, if you're growing trees for the next generation to work as lumber (or for an older version of yourself), remember: pruning pays off. There is plenty of room in this piece of oak, between the pruned branch and the bark, to make a chair leg or two. If the homeowner hadn't pruned this thing, probably about 1992, this piece of wood wouldn't have been workable today.