Hassan vs. Hussain

[At a hospital]
1 walks into and out of a room calling out “Hassan?” He looks around. “Hassan?”
2 looks at him but doesn’t initially react.
1 walks comes around again after a minute. “Hassan? Hassan?”
2: Hussain?
1: Hassan?
1 shows 2 the requisition form.
2: It says “Hussain.” There’s a difference between Hassan and Hussain.
1: Oh. I didn’t know.