The veil of the temple was 3 inches thick and if you study out the veil and the history of the temple, you will find that it was the spirit of God that did the transferring. Just as when you or anybody really prays beyond the flesh and enters into that secret place with God so it is with the holy of holies. If you were not holy or consecrated unto God you could not get through the veil. Not once is a high priest killed in the Holy of Holies if you study it out you will find that.
The priest would wait at the veil and God would transfer them from one side to the other by means of his spirit "only" if they were holy and he accepted them because of it. If he did not except the sacrifice the priest couldn't even get through the veil. Its a wonderful experience because the priest had to have blood in one hand on a laver and a incense in the other to sprinkle the blood on the ark and to offer the incense as a sweet prayer from the people. Neither could touch the ground and there is no opening in the veil contrary to belief so the spirit of the Lord did it.