a mote in the eye of a person you're talking with

hello nicanorr... i have been in this situation before. i was talking with my mentor/teacher about something very serious. i have great respect for this man because of his generosity and wisdom. while we were talking i was not looking at his face at all i just concentrated on his voice and on what he was saying. but when he finished talking and it was time for me to say goodbye i had to look at his face and his eyes but to my surprise i saw a big mote on one of his eye. i can't exactly remember which eye because i had to hurriedly look down so he won't see the surprise on my face. i did not have the heart to tell him there is a big mote in his eye. i just ignored it and acted like as if everything was normal.