There are many verbs that are designated for a special limb or special noun, and with these verbs we do not need to mention the limb or noun that performs the action of the verb, unless it comes to be precise.

Likeוילך ברגליו (and he walked with his feet), וישמע באזניו (and he heard with his ears), וירא בעיניו (and he saw with his eyes) - the noun is superfluous. And it means to say that he walks with his feet and not on a horse, or that he himself hears and sees, not through others.

לבטא בשפתים (swear clearly with his lips)³⁹ - to exclude swearing in his heart.

footnotes: ³⁹ Leviticus 5:4.

לא תגיע ידו (if his means suffice not)⁴⁰ – his own means.

footnotes: ⁴⁰ Leviticus 5:7.

וסמך ידו (And he shall lay his hand)⁴¹ - not through an envoy.

footnotes: ⁴¹ Leviticus 1:4.

במלח תמלח (shall you season with salt)⁴² – not to salt in salt water.

According to the Malbim, there are no truly superfluous words in the Written Torah (Rule 238). Every word in the Torah is there for a reason. Therefore, if the Torah says “he heard with his ears”, there must be a reason why the Torah mentioned the seemingly superfluous “with his ears”. In such an instance, it would be to exclude the possibility that he heard through others.

footnotes: ⁴² Leviticus 2:13.