I never used canned cat food without the pull rings, yet, my cat will come to the sound of the can opener...DNA? Previous life? (1-8) or TWILIGHT ZO-AN?
I think it has something to do with teh sound.
The sound itself is strange, and they have to check it out.
And they show up to find their pet humans holding this thing that is buzzing, so they stare at us like we've gone cracked.
Eventually they figure out that buzzing means 'food'.
This gets handed down, passed from generation to generation.
Much like the tale of great-great-grandkitty "Captain Shanks" taking a spin in the dryer..