Because of the ratio between the height and width of the minarets and the width of the eivan, if you climb into one minaret and shake it, the other will shake in unison. This constant shaking has been responsible for considerable structural damage, although this is locally blamed on British interference! You can experiment with the phenomenon on this site by clicking on the left minaret in the image above while will make the right one shake - although rather more than the real ones do!
There is another pair of shaking minarets built during the time of Oljeitu, at Oshtorjan, although these have lost the upper two thirds.
The wooden beams on the upper part of the minarets have been placed there to facilitate the shaking of the minarets, but the presence of wood in the brickwork causes other complications. Shaking is in theory restricted to once every twenty minutes, however, particularly during holidays, there is a constant stream of visitors who experiment with the phenomenon, and the visitor will have ample chance to observe it from ground level, without running the risk of being blamed for any further dereliction.
According to Honarfar, the porch is 10 metres high and 10 metres in width, the minarets are 7 metres taller and are 4 metres in circumference.