Ben, again you have sent us some interesting questions!

1) We brought the Bar Yochni bird first because this is a suggestion based on logic, which is easier to make than a suggestion based on tradition. To say that it refers to a human face would require us to have a Gezeirah Shavah, which only Rav Acha bar Yakov told us about. The Gemara in Pesachim (66a) tells us that a person cannot formulate a Gezeirah Shavah on his own; one must have received the Gezeirah Shavah from his teacher. The Gemara says there that one may formulate a Kal va'Chomer on his own, because a Kal va'Chomer is based on logic for which one does not require a tradition. Therefore, we tried at first to learn from the Bar Yochni bird, which appeared to be quite a logical move, until we rejected this approach with "Tafasta," which is also a logical concept (see Tosfos DH Tafasta). Then, when we tried to learn from the smaller bird, which also is a logical tactic, we were able to deflect this only by using a "card" of a higher "trump value" -- namely a Gezeirah Shavah, for which the tradition actually goes all the way back to Har Sinai.

2) I found that the Mesivta edition of the Gemara cites the Zera Yitzchak, by Rabbi Yitzchak Ataya, who asks your question on the next stage of the Gemara: Why does the Gemara ask from the angel face when it should have been obvious right from the beginning that we are going to reject it with "Tafasta"? The Zera Yitzchak gives a thought-provoking answer. He asserts that the Gemara often asks questions to which it knows that a certain answer can be given, but it wants to try to see if there might be alternative answers that could also be given

Here, the Gemara knew right from the beginning that the question from the angel face could be answered with "Tafasta" but it wanted to know if there were any alternative answers. When the Gemara could not find any other possibility, it fell back on "Tafasta" which we actually did know right from the beginning.

1) I found an explicit Tosfos in Shabbos 43a (DH Kofeh) who says the same idea as the Zera Yitzchak that I cited above in #2. Tosfos there writes that when the Gemara asked its question it knew already the answer that could be given but nevertheless it asked in order to see if there is another possible answer that could be said.

2) However I also found that the Aruch la'Ner, by Rav Yakov Etlinger, asks your question and gives a different answer. He writes that there is a difference between before we know the Gezeirah Shavah of Rav Acha bar Yakov of "Pnei, Pnei" and after we know this Gezeira Shavah. Before we know the Gezeirah Shavah we were forced to give the answer of "Tafasta," but once we have the Gezeirah Shavah perhaps "Tafasta" is no longer an acceptable answer.

3) The Aruch la'Ner questions his answer from the fact that "Tafasta" was an answer that was already given on 5a, well before Rav Huna was ever mentioned. This seems to suggest that "Tafasta" is a Sevara that is accepted by the Gemara. The Aruch la'Ner answers that one could say that the Gemara on 5a is following the idea mentioned in Tosfos on 5b (DH Tafasta) in the name of Yesh Mefarshim that the rule of "Tafasta" applies only when there is no upper limit to the higher possibility. Here, however, we learn from Rav Huna that there is an upper limit, because we are deriving now from utensils that could fit into the Mishkan. Indeed, it is from the fact that the Gemara is discussing here utensils that could fit into the Mishkan that Tosfos on 5b (DH Tafasta) refutes the opinion of the Yesh Mefarshim.

Kol Tuv,

Dovid Bloom