Regan's Straps
Regarding the second half of the movie where Regan is literally strapped to her bed while fully possessed -- could the demon actually break free of these straps if it had wanted to? There's a shot of someone's shadow (presumably Miss Regan's) gliding across her bedroom window, seen by Kinderman from the street as he stakes outside the house. This implies that Regan can move about as it wants, even after being strapped.
The demon also asks Karras to undo the straps for it.
If it could undo the straps, why wouldn't it have done that to mess with Chris and the others caring for her? I feel like it could have lashed out at any moment if it had wanted to.