You notice that they are walking on a sheet of ice between 10,000 and likely 13,000 feet high on Mt. Shasta. It's hard to breathe.

You notice that they are carrying ice axes (which can save your life in situations like this

 (AND) they are wearing Crampons on their climbing boots so they don't die on this kind

 of slope. So, the challenge (mostly) beyond good coordination is to not pass out while 

climbing because of a 

lack of air. I found in climbing the mountain in 1970 that I had to take about four breaths

 per step and this increased

as you move past 10,000 feet to 12,000 and 14,000 feet. If you try to walk like normal you

 will get Air Sick (not enough oxygen)

and then you will have to have someone rescue you or climb down yourself throwing up

 all the time. So, being fully aware

you are getting enough oxygen every step is one of the ways you successfully climb a 

mountain. There are many things

that can go wrong and any one of them (or combination of them) can and will kill you. So, 

if you aren't taking all this very seriously

it will be the last thing you ever do. Also, being roped together is only as useful as your

 weakest climber. Even one 

weak climber can kill all the rest when you are roped together in situations like this.

Also, I just noticed something else. Originally I thought the three people were resting. 

Well, they might be doing that too but mostly what they are doing is belaying the three standing.

Why? So, if one of the standing three falls and slides they can prevent hopefully everyone 

by belaying them with the rope. Then the sitting three get up and the standing three sit and belay 

And so on up the mountain to the summit.

Though I was with 3 other guys in 1970 I summited alone with an ice axe and crampons and 

no rope at all. Two of the others summited like I did that day. Then around 4pm in the afternoon

before the sun set I mostly slid down on plastic on the snow using my ice axe as a brake. I wouldn't recommend this

for everyone because it is dangerous. But, then again all things you are doing like this are very 

dangerous. I would say it is equally dangerous as SCUBA diving or Surfing in it's real danger.

I was sliding at about 15 to 20 miles per hour dragging my ice axe but now I'm not sure I would recommend

it simply because they don't usually strap the ice axes to your wrist because people have died doing that since 

then but it worked fine for me in 1970. Things change a lot over the years.

Hotlum Glacier Climb Teams