http://www.bcnscuba.com/
Yah, those are hook knives.
As a Jumpmaster, I've had my hands on all sorts of hook knives.
The Italian hook I saw looked like it'd take a 3/8" line in the wink of an eye, by far the best blade I've seen in over 25 years of parachuting. (or 35 yrs of diving).
"Innovative Scuba Concepts" has them, they're made by an Italian outfit.
http://www.innovativescuba.com/
sn# TM-1601
comes with sheath, 7-1/2" long, $10 - $12 retail
They're not pictured on the web site, & you'll have to go through your local dealer to get them.
The major distinguishing factor about these knives is the use of semi-serrated razor blades, it looks like it would have no trouble zipping through a tree branch, not to mention a piece of line.
If you can't find a shop to order the critters for you, give a yell. I'm going to be getting some of them for myself.
Another source for hook knives is a parachute supply house, one that I've used quite a bit is PARAGEAR.
http://www.paragear.com/default.asp
Look under "accessories", and then select "knives".
The Italian knife I mentioned looks like the "Jack the Ripper" but with serrated stainless blades.
Happy Hooking...:mean: