In the scene where the guy is showing Tom Hagen his $600,000 horse Khartoum, it has a white patch on his head. Whenever the guy wakes up to find Khartoum's bloody head in bed with him, there IS NO white patch.
what happened is that originally they had a fake horse head for the bed scene... apparently, however, it didn't look right. they had to go to a slaughterhouse and get a real horse head... of course, with such small notice, they wouldn't be able to get a head identical to that of the live horse... and you can't expect them to kill the horse used in the earlier scene...