Ok, another two things, one of them being really strange:
1. When I tried shooting at the ketchup cup after giving it back to Sybil, Sam "aimed" at it for a really, really long time (action (like Sybil drinking) went on, so I guessed it wasn't like loading or something)
. I clicked around (not having a cursor or something), and when Sam eventually fired -- before he did, the gun in his hands shrunk?! I know, this sounds crazy, and I really tried to reproduce it by doing the same things again, but it didn't happen again
2. After trying to reproduce the latter bug several times and clicking quickly through the subsequent dialogs, I had Sam still having a muzzleflash right at his feet. When he walks, it stays same distance from his hand, always coming along with him. After leaving the scene, it was fixed.