With SHA1 the chances of that happening are so close to zero that you'd have to create trillions of keywords before you even approach a minuscule chance of hitting a collision.

One of my favorite analogies for SHA collisions: http://stackoverflow.com/a/4014407/690258

If you find a hash collision, let us know. As security people, we'd be very, very concerned if you can find even one collision or even engineer a collision in SHA1 or especially SHA256.