The clip is never shown on the safety demo masks so pax are unaware of why one has to pull on the mask.
Depends on the operator. Some explicitly mention that you have to pull the mask towards you to start the oxygen flow, some don´t. Even for those who tell you, I believe that 80% of the passengers don´t understand, what they have to do exactly.
The better safety briefing would be the following (found somewhere on the web years ago) :
In case of a decompression, oxygen masks will drop from the ceiling. In that case, stop screaming hysterically, pull a mask towards you and place it firmly over mouth and nose, and breathe normally. If you travel with a child, assist him with the mask. If you travel with more than one child, you should decide now which one you like best.
I noted in some aircraft, that the oxygen masks are more or less located straight above your head. I fear, that a lot of pax would grab the masks above the head of the passenger in front of them, as this is the one you can actually see. In that case, the rearmost set of masks will not be used, and the front row passengers will have a problem.
The safety briefing for emergency exits is also depending on the operator. British Airways does a detailled briefing, the FA removes the handle cover to show you the opening handle, remarks that the door is quite heavy, and tells you that you have to throw it out of the opening.
Lufthansa just have pictures on the seat back close to the exit, no briefing is done.
Checking in at JAL you get a leaflet, that tells you you are seated at an emergency exit, and you should ask the FA for a briefing. When asking, the answer is "don´t touch anything".