Rav Sadya Gaon: In your hidden place.

Rashi: In your thoughts.

Ri Kara: When you are alone.

Rashi: Even [in your thoughts, without speech]. Metzudas David - do not say that no one knows your thoughts to inform on you to the king. Someone will understand from a gesture, and tell him.

Ibn Ezra: Even if the king is a youth (16).

Seforno: Even if you know that the king and officers will ruin the country via their bad conduct [do not curse, lest it cause harm to you].

Bava Basra 4a: Herod disguised himself and tested Bava ben Buta; he suggested that Bava curse the king. He refused, due to our verse.

Rashi citing Koheles Rabah: Do not anger the King of the world.

Rashi: Do not curse a mortal king.

Ri Kara: When people rejoice amidst drinking wine, sometimes amidst inebriety they talk bad about people. Do not do so, lest evil come to you! This is not only amidst other invitees who can testify about you; also when you are alone.

Metzudas Tziyon: "Tekalel" is an expression of Kalos and disgrace.

Bava Basra 4a: Herod told Bava ben Buta that he may curse Herod, for he is not really a king! Bava refused, for even so, one may not curse even an Ashir.

Ibn Ezra, Metzudas David: Also an Ashir [do not curse], for he can harm you with his wealth.

Ri Kara: Do not say, it is no problem to curse an Ashir - "veha'Kesef Ya'aneh Es ha'Kol" (19) - all need an Ashir. Also you will need him!

Bava Basra 4a: Herod told Bava that he may curse the king, for no one will tell the king. Bava refused, due to our verse.

Rav Sadya Gaon: Believe that a bird will spread the words.

Rashi: The Neshamah put in you, which in the end will fly to Shamayim.

Ibn Ezra, Rid: This is a Mashal, like "Ki Hi Sham'ah Es Kol" (Yehoshua 24:27; it refers to a rock). Metzudas David - the king will find out quickly, as if a bird brought the voice of the curse to him.

Rashbam, Ri Kara, Rid: It is impossible that the matter will not be revealed; in the end, hidden matters will be revealed.

R. Avigdor citing the Targum: Do not curse an Ashir, for the angel Razi'el announces on a mountain, and the voice goes throughout the world. R. Avigdor - an angel stands above a man's head, and makes heard his deeds and speech to an angel much higher than him, and [the latter] bring it above. Angels ¹ are Sheluchim (messengers) - "va'Yshalcheni Hashem Leshachasah" (Bereishis 19:13). Hashem's Shali'ach is like Himself - "Ki Mashchis Hashem Es ha'Ir" (ibid. 14). This is why it says "Al Temar Bo Ki Shmi b'Kirbo" (Shemos 23:21).

Seforno: The motion of the air will bring your voice to someone outside. He will hear it, without your knowledge.

Rashi citing Koheles Rabah: The angel that accompanies you - "Ki Mal'achav Yetzaveh Lach" (Tehilim 91:11).

Rashi: Passersby; you should fear lest someone hear.

Ibn Ezra, Rashbam, Metzudas David: It is a bird; the matter is repeated.

R. Avigdor citing the Targum: Eliyahu Kohen Gadol flies to the Raki'a [like an eagle] with wings, and shows matters done covertly here, to all who dwell on the land. The Hei in ha'Kenafayim is extra. It hints to five transmissions [of his deeds] when he sleeps at night - the Neshamah tells the body, the body tells an angel, an angel tells a Keruv, a Keruv tells Ba'al ha'Kenafayim ha'Serafim, and Ba'al ha'Kenafayim tells Hashem. The Neshamah has five names ¹ , and it is like a Chagav (locust), which has wings. The Gematriya of "ha'Shamayim" equals that of Neshamah.

Seforno: It is someone who will speedily tell the king that you cursed him, amidst hope for reward - nothing is withheld from the king (Shmuel II, 18:13).

Refer to 10:20:6:4.

Seforno, Metzudas David: That you cursed the king.