Looking at the video Matt posted, it looks to me like a sawtooth pattern is made in the can--a series of straight punctures connected in a zig zag pattern. So I'm not sure we've really nailed down how the can was opened. Chris mentioned a lever type can opener, and it would be interesting to do an experiment to see what kind of pattern you get from that. It was also mentioned that pocketknives often have a can opener and to me the pattern looks more like a pocketknife canopener. Ric mentioned that a part of a knife was found and he didn't think that knife had a can opener, but first of all I'm not sure how definite that is since he only found part of the knife. Also, the knife part he found may have nothing to do with the can he found. The knife could be the castaway's and the can could have been a coast guard discard that some coastie opened with his trusty pocketnife that had a can opener. Guys and pocketnives kind of go together after all, and if I were going to serve on a remote Pacific Island I think I might want to bring a knife with a couple of useful attachments like a can opener.
Anyway, I would suggest we all go out and cut open a few cans a few different ways and report back here. Maybe Matt's suggestion a previous post that even a P-38 could produce the observed pattern could be tested. P-38s are availble on eBay, as are lever-type can openers.
BTW: anybody find a label that fits the can Ric posted?