What is the significance of Faustus' blood congealing in Doctor Faustus?

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robertwilliam eNotes educator| Certified Educator

"My blood congeals and I can write no more".

 Thus speaks Faustus, on trying to sign his contract with the devil, which Mephistopheles has told him already, has to be signed in blood. The second time, Mephistopheles brings fire to dissolve the blood and allow him to sign, but not before Faustus has considered the congealed blood as an ominous sign:

What might the staying of my blood portend?
Is it unwilling I should write this bill?
Why streams it not that I may write afresh?
Faustus gives to thee his soul.
Ah, there it stay`d. Why should`st thou not?
Is not thy soul thine own? Then write again.
Faustus gives to thee his soul.

Is it a scary moment designed to warn Faustus at the last moment before it's too late? Who knows what to think of it - but it's a significant moment in the play: it marks the last chance Faustus has to go back on the deal.