My rat lost a nail and it's bleeding. What should I do to stop it?

Ouch, that can be a very painful condition when the raw nail bed is exposed or the nail isn't completely torn off. The nail bed does tend to bleed a lot. The best way to stop the bleeding is Styptic powder or Kwikstop, which are used for dogs who had their nails trimmer too short on accident. If you have some of that around, pour out a a bit (around 1/4 or 1/8th teaspoon) and dip your rat's bleeding foot/toe in it, then apply light pressure. You may need to repeat that a few times.

If you don't have an styptic powder, do the same thing with flour or cornstarch. It will take a bit longer to stop the bleeding.

Finally, if you can't stop the bleeding, he's limping, won't eat/drink/rest normally, or the bleeding keep starting again, he'll need to go the vet to make sure he doesn't need pain meds or antibiotics and to make sure the nail is fully removed.

Good luck!