In John's account, on what was the sponge of sour wine lifted to Jesus' mouth?

Answer: A stalk of hyssop

They soaked a sponge in sour wine, put it on a stalk of hyssop, and lifted it to his mouth. Then Jesus said, "It is finished."

“A jar of sour wine was sitting there. So they soaked a sponge in the wine, put it on a stalk of hyssop, and lifted it to His mouth.”— John 19:29 (BSB)