Why in my folder Inbox appear 2 unread emails, although there is no email unread there?

My folder Trash is empty, in Bulk there is no unread message.

Why in my folder Inbox appear 2 unread emails, although there is no email unread there?
I have no idea why that happens, but it happens all the time with me. Just go next to where it says..."View: All Messages" and click on that sideways triangle tab. it will give you the option to view ONLY unread emails. When you do that, you'll see the unread emails that didn't show up. I have to do that at least once a month.