A colleague called me to confirm some numbers with her before a meeting, just some simple multiplication, easy arithmetic stuffs. I was in line so I had to do it in my head, so I made mistakes and said, “uh, hold on a sec” and “wait, that was wrong” a bit. Then I heard a snort from behind me in line. When I turned around, an older lady was smiling. Oops! I smiled sheepishly in return.