Behold produces a log file that reports any errors and warnings Behold encounters when it reads the data from a GEDCOM file. It saves the log file in the same directory as the input file, and gives it the same name with ".log" appended to the end.
Behold does not display the log file by default, since you will not need to see it too often. But it is useful to look at it the first few times you load new data, so you can go back to the original data source and correct any problems Behold might have found.
To view the log file, you can either select "View Log File(s)" from the View menu, click on the log file icon on the toolbar, or press the F11 key. This will open up the log file using the default program for text viewing for your computer. Usually that is Notepad.
If you have more than one GEDCOM loaded then several log files will open - one for each GEDCOM.