In the software field, Black-Box testing is performed when an engineer is examining a closed system without any knowledge of its inner workings.

That being the case, do we have any documentation of how Tefillin works, from our limited knowledge of what happens inside the Shel Yad and Shel Rosh?

This question is Purim Torah and is not intended to be taken completely seriously. See the Purim Torah policy.

  • Rashi or Rabenu Tam?
    – Shalom
    Feb 18 at 11:22
  • Pashtus the same test the Gemara Shabbos (bama isha) says to use to test amulets; though truth be told, the Gemara then distinguishes between herbal and scribal ones, so maybe it's not a truly black box.
    – Shalom
    Feb 18 at 12:36

The internal protocol by which tefillin communicate during tefilla is not known. This is an example of well-designed component architecture. While it is given to us to know certain things about the public interface of tefillin (the four Torah verses, the straps, the calf's hair, etc), and the design is sufficiently polymorphic to allow for more than one object with a compatible interface (both Rashi and Rabbeinu Tam), we cannot break the encapsulation and know how they internally work. The documentation indicates that:

And it shall be for a sign for you upon your hand, and for a memorial between your eyes, that the law of the LORD may be in your mouth; for with a strong hand did the LORD bring you out of Egypt.

This tells of their functionality, so that we may use them without ignorance of their purpose, but how they accomplish that task is not our concern. Indeed it is possible that the internal mechanism of tefillin has been changed multiple times if it were the will of Ha Kadosh Baruch Hu, but because the public interface remains unchanged, any upgrades (or let's be honest downgrades) to the internal protocol should not effect our usage of them.

It is known, however, in the name of Rav Joel Spolsky, that all abstractions are inherently leaky. Actual implementations in the real world will always show behavioral details and differences that are not intended. For example, the Rambam writes that:

As long as the tefillin are on the head and on the arm of a man, he is modest and God-fearing and will not be attracted by hilarity or idle talk; he will have no evil thoughts, but will devote all his thoughts to truth and righteousness.

I can tell you from experience that this expected behavior does not work on all people at all times. Similarly, we have stories of sages of the past using tefillin to drive away demons or protect women in childbirth. Given the encapsulated nature of the internal tefillin protocol, we cannot know if all tefillin or our tefillin support this advanced functionality.

This shows how your notion of "black box" testing can be quite useful in telling us some information that is not captured in the documentation. Thus far we have mainly used anecdotal testing of tefillin in specific scenarios. We can tell when their use as a sign is effective. We have some non-statistical evidence of their use to enhance tefilla or expel demons, but a rigorous testing framework has not yet been developed. It may be that you are just the person to undertake such a task so that we could then discern which tefillin or which people at what times are able use the more advanced functionality.

I leave it to you to work out the details of how to implement such a large scale testing framework, and wish you kol tov, and a freilichin Purim.


This is also easy.

We know to "search the Torah over and over, for everything is in it". Everything obviously includes all software, firmware, wireless, and technology, which is, was or could be. So we should not be surprised to find that hidden within these strange objects, is some very advanced technology, whose functioning at least we can deduce much about.

Indeed, inside the Tephillin, we do find writing of a prescribed fixed nature, not a dot or comma of which we also know, may be changed. The writings within, are clearly some form of advanced software, probably designed to interface precisely with the hardware - which not uncoincidentaly, is also highly prescribed.

Attached to each of the hardware items are two long cables of an organic nature. We know that the body produces electricity and that voltages develop between different parts of the body. The cables are of an absorptive durable flexible material that will tend to absorb sweat - a form of salt water, or in other words, a conductive medium. The other side is dry and covered with a dark insulating film also organic in nature. We know that batteries stack cells to built up ample voltage, so we should not be surprised to find a complex construction of stacked layers, again in a prescribed layout, at least at one cable end. Hence why we have a redundant setup, but both have long cables. The cables probably also house the antennae or whatever is used - AC on a DC voltage would mean the same conductive layers could be used, but this isn't verified.

So tephillin are actually microcoded mini broadcasters with power cells. You would need to disassemble/decompile the writings within, to understand their purpose.

We do however have some hints to go on.

We may deduce that the Shel Rosh contains RAM, based on the verse that states this one shall be as memory between your eyes. Likewise, the Shel Yad is the main broadcasting hardware ("You shall bind it as a sign - or signal - upon your hand"). We may further deduce from the expression that they shall be as totafot between your eyes, that totafot is some type of VR display with stereoscopic vision (but Ben Zuma states it is a discount voucher for Amazon Prime).

The writings state that the "commands" they contain should be obeyed - clearly this is the invoking script for the rest of the software.

If this happens, the script continues, then correct functioning can be tested by checking a standardised signal is detectable that will be received via other Tephillin, and which only "Israel" can detect ("Hear Oh Israel").

  • Nice! Reminds me of an old Sheindel Weinbach story, "The Project," portraying the construction of the Mishkan as a method of beaming in on transmissions from beyond.
    – Meir
    Feb 17 at 16:36

Yes, this is very simple.


  1. Attach positive lead from high voltage power supply to right end of shel rosh strap.
  2. Attach negative lead from high voltage power supply to left end of shel rosh strap.
  3. Gradually increase the voltage until the mispallel is in danger of swallowing his tongue.
  4. Politely ask the mispallel to say Shem.
  5. If the mispallel is still conscious this is a sign that he is a true oved Hashem.
  6. If the mispallel has fainted, then check his tefillin and try again.

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