Sounds like the Chinese Water Torture :wideyespukingdog said:Yep, as Spyglass1 says.
My preference is a coffee cup of water in the microwave for maybe 4 mins, dip the head in to the shouders. Pull out after a minute or so, and the head will come off easily. The softness will abate as the head cools. When you remount the head, there's a notch in the neck opening and a key on the neckpost.