The rest of the hour was spent exploring that twinge, and then searching for exercises that don't touch my shoulders. Which is hard. Everything, almost, goes through or gets stabilized by the shoulders. Especially exercises that touch the arms, the chest, or upper back. (It's already very hard to exercise the chest, it's impossible to isolate, and the muscles in the shoulders are much smaller, and so give out long before the chest itself is tired.)
On the plus side, the twinge looks and feels like it's "just" a small muscle strain, rather than connective tissue damage. Muscles heal in only a few weeks, while things like tendons and joint cartilage take practically forever to heal.
But still, in the meantime, that still means a whole week, and maybe two, of no heavy loads through my upper body.
(Weird, according to emacs ispell, there were no misspelled words in this post. I'm not so good at spelling, I've almost never been able to spell this many words in a row without screwing up. This means, of course, that instead of a spelling error, there is instead a horrible glaring error of grammar that I will not notice until after I've posted it and y'all have read it.)