As my family has ties with the University of Leiden I used to hear stories about Einstein.The uncle of a friend of mine received extra lessons in math from Einstein, together with a son of Ehrenfest (?). He remembered that problems became clear and simple when Einstein explained them. Also, he still saw Einstein and Ehrenfest trough a low window, discussing for hours on end, writing furiously on a blackboard. Einstein wore a turtleneck sweater on such occasions, which was somewhat bizar in that era.