Things were easy when Henry only had a few simple words. Words like "apple" are easy to say and hard to mistake. Words like '"banana" were a little tricker, but once you knew that "numna" was "banana" you were all set.
Now that he is learning more complicated words like helicopter and dump truck and stringing multi-word sentences back to back things are getting much more dicey. If you don't have context he is almost impossible to understand. If you add in all of the words that he just flat out makes up forget about it. Sometimes I think he is just screwing with us for laughs.