Wow, so this is trippy

I just realized this...

In class, my professor has been saying "yisi shi(r)" but I've been hearing "is assured"

What's weird about that? yisi shir means "meaning".

So for example, he'd say (forgive the shoddy english, I'm dealing with Chinese here..) " 'Am not one of the best students?' yisi shir she is one of the best students"

And I was hearing: " 'Am not one of the best students?' Is assured she is one of the best students".

Com'on. That's trippy like 13th Warrior language learning trippy...

Anyone?