If he just ate it you will need to get him to vomit that up. Give him either 2 tbsp of table salt by mouth or 1/3 cup hydrogen peroxide by mouth now. Within 30 minutes he should vomit and watch to make sure you see it in the vomit. If you're not comfortable doing this get to your vet asap as time is important in toxicity cases. They will most likely put him on an antidote for rat poison as well, Vitamin K1. Time is of the essence.
You did great. I would wait until the vet opens this morning and get the Vitamin K1 shot and capsules to take at home. Just be there when they open.
Great! I'm so glad it worked out. Time is so important in toxicity cases. Tell Tiger to stay out of trouble!