Episode Details

If one who is in the process of laying tefillin makes the blessing on the arm, puts the "tefillin shel yad" on, and then speaks, interrupting himself before laying the "tefillin shel rosh," what must he do? Make a new blessing? A different blessing? Is he fresh outta luck? Also, what was the timing of laying tefillin - from when until when? Plus, the parallel between the laying of tefillin at night and on Shabbat (and yom tov). Also, the significance of the "sign" that is tefillin.