Just think.
Right now at your local hardware store are tons of tools you can buy. If you need to cut something, you can buy a saw.
And when you use the saw, the word "saw" is the verb of how you use the noun. So you'd use a saw to saw.
And if you had an instinct to cut a saw in half, you might use a second saw to cut the first saw in half.
But you wouldn't do that. YOU have no desire to do that. But maybe someone else does. And maybe you just happened to bear witness to the cutting of the saw. You will have seen it. And since thats now in past tense, you saw it happen.
In which case you will have saw a saw saw a saw.