how to open a can without can opener

Jim Shoe wrote:
Well, there's three minutes of my life that I'll never get back. Just buy a P-38 or P-51 can opener at a military surplus store. You can carry it on your key ring and its a lot lighter than carrying around a block of concrete.

I used to carry a P-38 on my key chain, but after it opened and stabbed me in the leg a few times, I quit that.
I got mine out of a case of C-Rats in 1966. It is probably in a box around here somewhere...
Now, I carry a Leatherman Wave. It has a very good can/bottle opener.