mrdct, on 2011-November-02, 22:38, said:
I don't think the failure to ask a question can transmit UI, nor is it unethical.
16B1a says: <snip> as for example by a remark, a question, a reply to a question, an unexpected alert or failure to alert, or by unmistakable hesitation, unwonted speed, special emphasis, tone, gesture, movement, or mannerism, <snip>
I see that it says "for example", but failure to ask a question is different to the examples given. It goes to the trouble to say "failure to alert". It could have easily said "failure to ask a question" if it had intended that.
And, reinforcing that, 20F1 states: "During the auction and before the final pass, any player may request <snip>" (my emphasis). This makes it clear that to request an explanation is optional.