Our 6 month old pit/lab puppy was energetic and acting normal two days ago. I gave her a biscuit (it's a new bag) and two or three hours later she was throwing up. She became listless and completely uninterested in food right away. This came on very suddenly. Now she's having not just bloody diarrhea, but twice so far she has lost at least a half cup of blood, we think from her rectum. What can cause this?