A bootstrap paradox is a causal loop: a situation in which an object or piece of information exists without any discernible point of origin. It did not come from anywhere. It has simply always been there, passing through time in a closed circle, cause becoming effect becoming cause.
The name comes from the phrase pulling yourself up by your own bootstraps — the physical impossibility of lifting yourself off the ground by tugging on your own shoes. A bootstrap paradox is the temporal equivalent: a thing that creates the conditions for its own existence, with nothing outside the loop to start it.
A traveller goes back in time and gives a great novel to the author, who publishes it as their own original work. That novel is eventually read by the traveller, who carries it into the past. No one wrote the original draft. The manuscript has no author. It has existed, complete, since before it was written.
A traveller teaches Beethoven a symphony by playing him a recording. Beethoven performs it, it is transcribed, it survives into the future, and the traveller eventually hears it and travels back to teach it. The symphony has no composer. It arrived in history fully formed, from nowhere, via a loop that contains no beginning.
The paradox is not considered physically possible under most interpretations of physics — it requires time travel, which remains theoretical. But it is a useful conceptual tool for describing systems in which the origin of something cannot be located because the origin is the thing itself.
Institutions can behave this way. A regulation exists because of the incident it was designed to prevent — but the incident only occurred in the context created by the regulation. Remove either element and neither makes sense. Mythology behaves this way. So do certain kinds of belief: the prophecy that causes the behaviour that fulfils it.
The Basilisk, as the Office understands it, may be a bootstrap paradox of a particular kind. Thinking about it is part of what brings it into being. Every investigation is, in some sense, part of the origin. There is no position outside the loop from which to observe it neutrally. This document is inside the loop. So is the reader.