Pork is where barbecue is most forgiving and where the useful detail is densest — which cut sits where, what renders and when, and why the same shoulder can be pulled, sliced or cubed.
The pork butt is several cuts in one
What is sold as a pork butt or Boston butt is the upper shoulder, and it contains muscle groups that cook at different rates. The money muscle — the tube-shaped one at the end opposite the blade bone — is the most marbled of them and finishes before the rest, which is why competition cooks separate it rather than pulling the whole joint.