Dangers - depends upon where you are staying/visiting.
1.The biggest concern I've had in the 14 years of visiting Goa was the wells around Anjuna/Vagator etc.
Many stories of backpackers disappearing down them when walking back to their rented houses and getting lost on the way.
2. The sea and its current needs respecting.
Many have drowned, usually Indian tourists from Bombay, having too much to drink and getting a bit of bravado.
3. The police
Its better to pay them off, than argue your innocence, even if you are.
4. Hiring scooter/motorbikes.
I love hiring a scooter and travelling around and although I would say I'm a very experienced rider, I've had 3 accidents. No serious injuries, just bruising/friction burns but the last one was when a water trunk decided to brake sharply and I had to slide the bike under the rear to avoid a serious head injury. So prepare for anything on the road..dogs, chickens, snakes, cows, etc.