Masakazu Imanari that's what. Check this clip, listen to Gurgel's knee pop if you can hear it over the screaming. Those heel hooks are nasty.
Jorge Gurgel is fighting Diego Saraiva at next week's UFC 73. I hope Gurgel has a game plan in mind to protect the knee that Imanari's heel hook blew out, other wise I think it'll be a long time in rehab for Jorge because he's about to fight a man with a proven record of ending fights via heel hook.
Of course Gurgel has submission skillz too, but Diego's got no bum knee that I know of.