First: جَاءَنِي الْعَصَا وَغُلَامِي — both nouns nominative, estimated ḍamma.
Second: رَأَيْتُ الْعَصَا وَغُلَامِي — both nouns accusative, estimated fatḥa.
Third: مَرَرْتُ بِالْعَصَا وَغُلَامِي — both nouns genitive, estimated kasra.
Takeaway: Their roles and cases change, but the two source nouns look the same in all three sentences.