This episode marked the first prominent appearance of more than one Observer and follows the events that occur when one of them saves a girl from boarding a soon-to-be crashing plane.
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'Blight' is foreshadowing the use of the term by Thomas Newton in S2E10 - Grey Matters to describe the deteriorated conditions in the Redverse.
Observers are featured in the episode.
The simulated aircraft in 'Of Human Action' has markings on it that say "AUG B/12" and "RESCUE", foreshadowing August saving Christine Hollis from a plane crash in 'August'.
At the motel in 'August' where Christine Hollis is being kept, August brings Christine Hollis a meal in a paper bag with a Chinese dragon drawn on it while Christine is being kept hidden in a motel, foreshadowing the villains working in Chinatown in 'Snakehead'.
The mistake and interference happened in "Peter" when The Observer distracted Walternate from finding the cure for Peter and when The Observer saved Walter and Peter from the icy lake.
August is referring to when Walter crossed universes in "Peter" to save the other Peter.
We later learn in "Letters of Transit" that the Observers and their tech are from the year 2609.