Seems like every boa we've ever had in this house does this, whether they are taking live or f/t. They are fast as lightning on the strike and the constriction but really like to take their time about the actual eating.

Some of our boa's seem to guard their dead prey, looking around intently to make sure nothing is nearby and a possible threat to them once they settle in to eat. Some of them will not eat if you watch them too closely so we've found it's best once they have their prey dealt with to simply walk away and leave them to eat in peace or for some of them we put a dark cloth over their glass enclosure (seems to help them feel secure).

I don't know but maybe it's just a safety thing that they've evolved. Make absolutely sure your prey is really dead = prey cannot suddenly bite/claw/kick you back. Make absolutely sure nothing else is nearby = you won't get attacked by another animal while you are busy swallowing a large prey item and very vulnerable yourself. Make sure you are at the head of the prey = easier and faster to swallow which if you consider the size of some of the prey boas can eat, is a smart thing and keeps them from being vulnerable to attack any longer than it has to be.

When you think about how a boa lives in the wild, hunting on the ground and up in trees compared to how a ball python hunts, hidden away deep in burrow - it makes sense. A BP hits it's prey, pretty much it's safe to eat. The chances of some other predator in that same burrow aren't probably all that high. But a boa up in a tree or down on the ground, well the chances could be much higher than another predator is nearby or could wander by when it's eating. Since it can't slither off fast, or strike back easily, when it's mouth it's full of a large prey item - well it just makes sense to me that a boa needs the instincts to eat in a careful manner so it doesn't end up being something else's dinner.