How does a decomposed person see his body, his seat in Paradise or Hell, and feel bliss or torment, if nothing remains of his body but a single bone?

It is part of the belief of Ahl al-Sunnah wal-Jama'ah (the People of the Sunnah and the Community) that the torment and bliss of the grave occur simultaneously to both the soul and the body. The continuation of this torment or bliss does not require the body to remain intact. Allah the Almighty is capable of conveying sensation to decomposed or scattered bodies, just as He, glory be to Him, disposes of the world's elements and materials as He wills. Indeed, denying this constitutes a denial of Allah's power, عز وجل. It is incumbent upon the believer to affirm the news of the unseen, to believe that Allah is over all things competent, and not to delve into the "how" of these unseen matters, because the human intellect cannot comprehend their specific nature. As for "the soul being in a bird's spirit in Paradise," what is meant is that the soul of the believer – which is his spirit – will be in the crops of green birds in Paradise, and this may be specifically for martyrs. The states and abodes of souls vary according to their condition.