I have to agree with Major League based on the information given. My list would have added options:
1. intentionally smashed head (human)
2. unintentionally smashed head (human)
3. accidental smashed head with an object in cage, snake got free/ nerve twitches released it
4. head got caught between lid and cage, snake panicked and thrashed, damaged own head and died
5. snake died of something painful, mouth was gaping, jaw unhinged (giving caved in appearance), and 'goo' came from the mouth and simply collected on the head
Basically what we need to know is:
Show us the habitat, what was in it, how the lid is attached and anchored
Was the goo coming from the head coming out of an open wound or could it be the mouth? How obvious / pictures of the 'head trauma'
Who has access to the room