When there is only a single consumer, a poison message can completely block processing of the queue.

He ſummons ſtrait his Denizens of air; / The lucid ſquadrons round the ſails repair: / … / Looſe to the wind their airy garments flew, / Thin glitt'ring textures of the filmy dew; / Dipt in the richeſt tincture of the skies, / Where light diſports in ever-mingling dies, …

a poor, disconsolated, drooping creature

An undivided interest means that the tenant in common has a share in the whole and not ownership of a separate portion.