Latest update.
I went to the vet with both snakes, and the results are that, while Mila is ok (I brought her there just for a check up), Shiro has a beginning of an abscess.
I have seen with the lens the seepage, tiny really, but pressing the "bulb", it is visible.
The vet disinfected it, and gave me a prescription to follow, telling me to do so for 10 days.
After that, check up again.
I am relieved..and I hope he will be good again soon.

Cheers!