Answers:
Vindaloo has a blend of red chilis.more than one, so that's what make vindaloo curry so hot. The curry isn't hot until you add the vindaloo into the curry. Hope this help
Other Answers:
The pepper.
the amount of chillies within it, the peppers and the different spices they put within it
basically it is the chilly but if u see adjectives Indian spices will add for a while spiciness to the food.so when all of them r put together beside chilly u can imagine how hot it will nibble
the process! the chilles are dry heated until that time being mixed beside other ingredients