Using More than One Instance
Synecdoche is usually defined as using one instance. But we are in the business of writing well, not following definitions. The fact is, using more than one instance can help. And that's all that matters.
His pulse is thudding in his chest, his neck, his temples. (Mr. Mercedes, King, page 200)
King doesn't care about the price of eggs in China, who bats leadoff for the Toledo Mudhens, or if people call that synecdoche. But he cares about vividness, count on it. And that has to be synecdoche for his pulse pounding – if his pulse is thudding in those three locations, it's thudding everywhere.
A grammatical aside: When a list is in proper grammatical format (A, B, and C) it tends to look like a complete list. Meanwhile, synecdoche is never a complete list. So it might be no coincidence that King used "improper" format (A, B, C). The following uses A and B and C:
They [news reporters] were just diligently doing their job, covering mundane events – funerals and fires and fairs.
Taking my own advice, I would see if there were any other items I wanted to add to pretzel. Maybe not, but I should check.
#3. I walk around the room in my bare feet, looking for any food that might have been left on a table or on the floor, like a broken piece of pretzel or a stale potato chip.
That's more words than I wanted to use for this small plot point, but I think that's slightly better.
Are there any instances I want to add to 'kite string'? No!