In verse 65, it was said: الْيَوْمَ نَخْتِمُ عَلَىٰ أَفْوَاهِهِمْ (Today We will set a seal on their mouths). On the day of Resurrection, when comes the time to account for deeds, everyone will be free to offer any excuse one has. But, Mushriks, the practitioners of shirk, those who associate partners in the pristine divinity of Allah Ta’ ala, will declare on oaths that they never had anything to do with shirk and kufr: وَاللَّـهِ رَبِّنَا مَا كُنَّا مُشْرِكِينَ (By Allah, our Lord, we ascribed no partners to Allah - A1-An` am, 6:23).
And some of them will also say that they were free of whatever the angels had written down in their book of deeds. At that time, Allah Ta’ ala will put a seal on their mouths, so that they would not speak. Then, He will give power of speech to their own body parts, the hands and the feet, who will testify to all their deeds as court witnesses against them. As for the present verse, it mentions the speaking of hands and feet only. In another verse, mentioned there is the speaking of one's ear, eye and skin: شَهِدَ عَلَيْهِمْ سَمْعُهُمْ وَأَبْصَارُهُمْ وَجُلُودُهُم ' (their ears and their eyes and their skins will testify against them - 41:20). As for what has been said at one place: تَشْهَدُ عَلَيْهِمْ أَلْسِنَتُهُمْ (and their tongues will testify against them - An-Nur, 24:24), it is not contrary to 'putting a seal on their mouths' because putting a seal means that they will be unable to say anything out of their own volition. Their tongue will speak counter to their personal choice and will testify to the truth.
As for the question how these parts of the body would acquire power of speech, the Qur'an has already answered that by saying: أَنطَقَنَا اللَّـهُ الَّذِي أَنطَقَ كُلَّ شَيْءٍ (Why did you testify against us? - 41:21) that is, these parts of the body will say that Allah, who has given power of speech to all things endowed with the ability to speak, has also enabled us to speak.