Author Intrusion occurs when the author slips out of the current POV and adds information that does not directly connect with the POV's observations. I had a minor one today.
His end had slipped into the water.
He spotted his end thrashing in the water, out of reach.
The second sentence keeps the reader in the POV's head and it evokes a more active vision. Also, the words out of reach generate a feeling of apprehension. Uh-oh! How's he going to get it.