1 Prof. Jones: Well I'm not letting you take the Siege Perilous. It's a valuable historical artefact!
1 Merlin: It's mine. I made it.
2 Prof. Jones: It belongs in a museum!
2 Merlin: It belongs in my living room!
3 Prof. Jones: But it kills anyone who sits in it!
4 Merlin: What can I say? I get a lot of unwelcome guests.

It kills anyone who sits in it, except those destined to find the Holy Grail, which includes Professor Jones. But that was too long to say in the comic.

It would be quite the piece of furniture though. A real conversation piece. Until someone sat in it.

Interestingly, historically a conversation piece was a painting of an informal group portrait, usually apparently engaged in conversation in an outdoor setting. This genre of painting became popular around the 1720s, particularly in Britain and the Netherlands, and persisted for the remainder of the century. It was only in later years that the term came to be used to refer to an item that was interesting enough to spark a conversation.