Alien: The death of Parker

leading from

Alien : Making The Movie

and 

Alien: Yaphet Kotto played Parker

a) Mysteries of the third eye

Filming took place as usual at Shepperton.

As the Alien closed in on Parker, Yaphet noticed that its projected mouth organ was headed straight for the space between his eyebrows, rather than into his chest or neck.

He associated that with the spiritual eye, or the third eye, and this was the spot where the people of India applied red ash marks known as tilaks.

He wondered what this was all about and it irritated him that he didn't know what was going on.

Yaphet's mind screamed "Why is Ridley doing this? Why aim at the third eye. What was he, Dan O'Bannon and Ron Shusett trying to say "

When he went to see the dummy version of his head where the craftsmen were working, he went even so far as to ask "Why is this thing going towards the spiritual eye man?" 

Source: http://toutlecine.challenges.fr

b) Nick Allder's brain busting rig
 
What happens to Parker is simply a suggestion in the final film. 

Perhaps no more than three or four frames long. 

Over at Bray studios, Nick Allder actually took a casting of Yaphet Kotto's head, and then constructed a dummy skull out of fibreglass - except for a section of the forehead which was done in wax. 

Since it was going to be a very large closeup, he made a special rig so they could just mount the alien's tongue and make it dart in and out and hit a specific spot on the forehead piece. 

Inside the skull, Allder put real pig's brains; and then they put special little barbed hooks on the end of the tongue. 

So during the shot, the viewer actually saw it punch through the forehead and pull out the brain.

Yaphet Kotto's brain busting rig using a casting
from Ian Holme's head as a test, shot at Bray Studios.
(infor:http://www.zen171398.zen.co.uk/Alien%20%28page7%29.html)
 (Photo by Pat Lowry)

c) Yaphet's assumptions
When Yaphet went ahead with the scene, a curious a sense of depression was starting to set in as he continued with the scene and the spell eventually broke.

When he filmed the attack, he had hair in the scene, and when the alien bit through the head, the head seemed to lack hair and it was as if they had used a melon.

Whatever the effect consisted of, at least he felt a psychological release as if it wasn't really him or Parker, it was just something that seemed like a bald melon.

Source quotes

1. Yaphet Kotto: "As the Alien closed in on Parker I noticed that its projected mouth organ was headed straight for the space between my eyebrows, the so called location of the spiritual eye. Why was Ridley doing this? My mind screamed. Why aim at the 3rd eye what was he and Dan Obannon and Ron Schusett trying to say. Depression immediately started to set it as I continued in the scene, but the spell would eventually be broken. When I watched the filming of the attack, I had hair in the scene. When the alien bit through the head on a melon they used did not have hair. I felt a psychological release as if it wasn’t really me or Parker. It was a god damm bald melon! ( The yet unpublished Yaphet Kotto’s Alien Diary)
2. Nick Allder: What happens to Parker is simply a suggestion in the final film. I doubt it it's more than three or four frames long. But I actually took a casting of Yaphet Kotto's head, and then constructed a dummy skull out of fibreglass - except for a section of the forehead which was done in wax. Since it was going to be a very large closeup, I made a special rig so we could just mount the alien's tongue and make it dart in and out and hit a specific spot on the forehead piece. Inside the skull, I put real pig's brains; and then we put special little barbed hooks on the end of the tongue. So during the shot, you actually saw it punch through the forehead and pull out the brain. (Cinefex 1, p63)
3.  Yaphet Kotto: Now I don't know why Ridley did this, but when that alien's mouth came open, it was headed right for my forehead which is where the spiritual eye is supposed to be located. So when I saw the dummy version of my head where the craftsmen were, I said, "why is this thing going towards the spiritual eye man?" The spot where our Indian brothers and sisters have their red dots. Well that's where it was headed. Why couldn't it have gone into my chest or neck? That just pissed me off. (https://www.vice.com/en_ca/article/9kw4mz/guy-killed-by-alien-in-alien-now-believes-hes-seen-real-aliens)

The dead Parker, curiously sitting in a meditative position.