When the flood was finished, Noah came off the Ark with all his animals, and God told them to "be fruitful and multiply," which meant, of course, that animals should just keep f---ing until they rapidly transformed into a wide variety of new species, as illustrated in the diagram below:
You're probably looking at that diagram thinking it looks an awful lot like an animal evolving over millions of years. Um, no. This is a post-flood horse changing over a few thousand years. DUH! It's all explained very clearly in the fine print:
On further reflection, I think the creationists liken the little horse on the left to the Chihuahua and the big horse on the right to the St. Bernard. The problem with this argument is that the St. Bernard come from the Chihuahua. Differing breeds of dogs are like the tips of branches. What Creationists don't want to claim is that they are showing different species or that speciation can occur.