Questions about example sentences with, and the definition and usage of "Heads"

A: Saying that somebody is "heads down (working)" is an idiom that means that they are only focused what they are working on, and they are avoiding all distractions and not spending any time doing anything else.

"We really need to spend the next two hours heads down on this presentation so it will be ready in time." (we need to avoid all distractions and just focus on doing the presentation)

"The students were all heads down working away at solving the math problems." (they were working diligently on solving them and not talking or playing around instead)

A: 決まり文句ではありません。文脈はありますか？

A: heads up = look out, be aware of, pay attention to
example:
Heads up, there is a wall in front of you.
Look out, there is a wall in front of you.
Heads up, the paper is due tomorrow.
Be aware, the paper is due tomorrow.

heads up = literally, put your head up
example:
Why are you sleeping in my class? Everyone, heads up!
Why are you sleeping in my class? Everyone, put your head up off the desk!

Heads Up = a charade/acting game
example:
I just got Heads Up on my iPhone! Let's play!!!

Heads Up, Seven Up = a game usually played by children in class. I haven't played this game in about 20 years, so I don't really remember how it is played.
The teacher secretly chooses 7 students.
The teacher then calls out "Heads down, thumbs up!" and all the students put their heads down on their desks so they can't see, and put their thumb up on the desk.
The 7 secretly chosen students walk around the room and each chooses a heads down student by pushing their thumb down.
They sit back at their desks and put their heads down and thumbs up.
After all 7 students have chosen, the teacher then calls out "Heads up!"
The 7 students who had their thumbs pushed down then have to guess which of all the students was the one to push their thumb down.
It's a weird game and hard to explain.

A: It’s usually used as a warning like “look out.”

A: "Heads up" is a phrase to let someone know about something ahead of time. It's usually used when someone is about to throw something at you, and you need to catch it right away.

But it also be used for other things. Ex: Heads up, the history test is going to be multiple choice.

A: Check the question to view the answer

A: Heads up! That baseball is heading right at you!

I want to give you a heads up. We are going to have a test tomorrow.