Not sure if this is a suitable question for this exchange.

Me and a friend are debating what can be seen through a periscope consisting only of two 45 degree mirrors. My friend tells me that the walls of the periscope would be visible in the mirror the the user of the periscope could see due to the way light bounces off the insides of the periscope.

I was under the impression that the only information being received by the eye would be from the two mirrors I understand that light bounces off the walls in the periscope and it would come off the mirror that the eye could see. But I thought this information would be omitted and superseded by the information that is directly coming off the two mirrors.

Is my friend right about the walls of the periscope being visible in the mirror too? And could someone explain it to me?