When I was visiting Ellison he showed me some of his tropical pitcher plants that have fangs on the hoods, and explained that no one is really sure why they have fangs.
I thought about it and came up with a theory:
If a small lizard or frog or large bug fell into the pitcher and tried to jump out, the fangs would keep them from jumping out by poking them, causing pain, resulting in the natural reaction of moving away from the pain, back into the pitcher.
The fangs may be a way for the plant to keep things in the pitcher and not allow them to jump out.
Just a thought, I could be wrong, Im not an expert or anything