> “It is not that unusual to find pieces of type in the river,” Sandy said. “Particularly around Fleet Street, where newspaper typesetters would throw pieces in the water when they couldn’t be bothered to put them back in their cases.

Some assistant being lazy, or rushing to "finish" a task?

Or sorts that broke, or were worn out, and it was normal to toss things into the river?

Or a ritual? (Say, toss a sort into the river for the first page an apprentice sets, or when there's a press failure, or for superstition after printing very bad news?)