In quarter-comma meantone temperament, 11 fifths are flattened to make pure major thirds (5:4). The 12th fifth -- the wolf -- must absorb all the leftover error.
The wolf fifth (G# to Eb) is ~737 cents instead of 702 -- a jarring, howling interval that "bites" when played.
Click fifths around the circle to hear good ones vs the wolf.