There are snakes in Rila so watch out were you step. Especially when walking on rocks.
Some of the snakes are poisonous.
A friend of mine who was raised in a Rila village told me that you could prevent a snake bite by squeezing a piece of garlic on your feet. So, if you want, try it :)
It was sunny 10 minutes before traking that picture and 15 min after that :)
After all do not forget you are in the mountain. It is a good idea to have a sweater and a rain coat at all times.