a couple quick thoughts/points: intestinal parasites can cause bloody diarrhea/stools. where i am going with that is, you may want to have a reptile vet take a look. there maybe an underlying reason why your boa got constipated in the first place. most of the time constipation happens for one of a (or combination) couple things. impaction (from ingesting substrate or something of that nature). but most of the time, constipation is caused by certain percentages of dehydration which prohibits proper intestinal motility/movement. and the key is usually to find out why the animal (or human for that matter) is not intaking as much liquids as they should be to function properly. i have seen in my hospital, quite a few times, constipated iguanas, bearded dragons, snakes, dogs, cats, ferrets, etc. about 90% of the time, when we run, whats called a packed cell volume (checks for anemia or dehydration), it is above normal (indicative of dehydration of varying percentages). too large of prey item can cause constipation also, but is usually not an issue if the snake drinks and/or soaks in water regularly to stay hydrated and keep proper intestinal motility. i know i threw alot out there. but being in veterinary medicine, i am trained to speak from a medical point of view. it also, could have been a simple case of being a little too plugged up until it was able to be brought out artificially and now the blood is probably from the trauma of being backed up and the enema. i would just maybe think about getting the boa checked out, to be safe.
-----
retic is king of kings
1.0 Tiger Retic
1.0 Albino Tiger Retic
0.1 Striped Tiger Retic (het albino)
0.1 Salmon Boa
1.0 Albino Boa
0.1 False Water Cobra