*Doing a Peer Code Review of someone senior to me*

Me: This fix doesn't look like it will work, but maybe I don't understand. How does this fix the defect?

Senior Dev: *Blinks* It works on my machine

Me: But how does it work?

Senior Dev: It works when I run it on my machine...

Me: Do you know if this will fix the issue?

*Silence*

Never seen QA punt an issue back to development so fast.