Welcome to Yorkie Talk. I'm glad your pup is doing okay after getting into rat poison! Very scary.
Pictures need to be resized to post. Here is a thread with a little info on posting from a smart phone:
http://www.yorkietalk.com/forums/gen...-pictures.html
Where is the bump? Probably not related to the rat poison. You probably have to follow up with your vet anyway because of the toxin exposure. I would definitely have the vet take a look at the bump. Could be anything from a tick to a sebaceous cyst. Because of the size and how fast it appeared, I would have the vet take a look.