nineteen to the dozen

(talk / chatter) nineteen to the dozen {UK} (to do something at a great rate; most often refers to speed of speaking — to talk very quickly without stopping) — говорить без умолку, без конца, без остановки; трещать, тараторить

Example 1: He was a great conversationalist and talked nineteen to the dozen, without stopping.

Example 2: Janet was chatting away nineteen to the dozen behind me and I couldn't concentrate.

Also
talk twenty / forty to the dozen (rarely)

<...>The idea is that the rate of talking is so great that when other people say merely a dozen words, the speaker gets in 19. It’s also sometimes used to describe rapid heartbeat in times of danger, and to refer to other fast-moving or fast-changing things (like dogs’ tails): ‘Oh look at its tail! It’s going forty to the dozen!

The usual form is nineteen to the dozen; on occasion I’ve come across twenty to the dozen, but never forty. It’s now perhaps a little old-fashioned as a British expression, though you can still find examples in newspapers and daily speech.

Nobody seems to have the slightest idea why 19 is the traditional number to use here, but it has been in that form ever since it was first recorded in the eighteenth century. (worldwidewords.org)