I think Larry's statement was along the lines of "show me the evidence" - to which Mike simply interjected "ETFs". It's not unusual for the regulars to make such brief interjections. Larry didn't hear him clearly, though - likely because of the delay on Mike's side - and asked "what's that?", and ...

... o yeah, there was some of that earlier, too - but in the opposited direction. Mike had scolded Larry a bit for interrupting just a few minutes earlier - which I think likely had Larry on a short fuse when he felt Mike was then interrupting him.