Kurt and Fred don ski masks when they are kidnapping people, but they are mechanics, and their shirts have patches with their names on them.
At the beginning of the film, when the naked female screams, after finding out that her partner has been strangled, the other characters that are nearby in the lake at night don't hear her loud screams.
When the first male victim is wheeled into the hospital on a gurney, he then escapes briefly, but one of the guards that wheeled him in moments before doesn't notice that the gurney is empty as she walks by just after he escapes. Then, she somehow finds out that he is missing, and chases him briefly outside the hospital.