During the first threesome, you can see in the close-up shot of Erica that she's wearing panties and Larry's feet are on top of the covers. In the wide shot, she is bare from the waste down and his feet are underneath the covers.
The platter that Howard knocks over from the table while trying to untie himself is nowhere to be seen throughout until that shot only.
Crew or equipment visible
Shadow on Erica's right hand in the opening shot.
When Larry gets stabbed, the knife is clearly made of rubber. It can be seen wobbling just after the second stab.