What are the most dangerous deep bone thrombosis symptoms?

Pain and swelling: I assume you mean dvt. The most common symptom of DVT is pain and the most common physical finding is swelling. However, not everyone has these. If you have unexplained swelling with or without calf or thigh pain then a venous ultrasound would be indicated to look for a dvt. Sometimes even a ct scan or mrv is necessary. The bottom line is, if DVT is considered, then proper testing is required.