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As a kid I imagined it to be a series of horrible flaps on its belly.

I agree, I liked it better too, because it was so not a guy in a suit.

But also because it's pale, like a maggot, or a thing from under a rock, something we have a natural aversion to. Not an insect or reptile, but a worm. I think the Hammerpede was a reference to that.

Moves the same way a snake would.

@Aorta

Series of flaps, whoa! I agree, it brings up this primal disgust.

@S.M

How so? Snakes jet across tables with tails in the air? Sorry, I don't see it.

It makes a flappy sound.

*squishsquishsquishsquishsquish*

It's undulating.

While squishing.

The wee bugger has it's own mini railtrack!

Maybe it uses squirt propulsion. (Pardon my French there XD)

Hence the squishy flappy sounds.

Well when it is "birthed" it's always covered by the blood of its host so maybe that gives it more traction to move in the way it does, at least at first when we see it on screen.

Fart propulsion!

This is another example of filmmakers making something that looks cool, but applying very little thought to explain the imagery. In Alien the Chesbuster literally zooms across the table its body upright, and its tail flapping furiously, with only a small part of its underbelly in contact with the table surface. But how...

Undulation - comes in two forms, side to side like a snake or up and down like a caterpillar. Side to side we do not see on screen, but up and down could be a possibility, but would require some amazing muscles in the creature's underbelly considering the small area in contact with the table.

Jet Propulsion - or Squirt, or Fart. A possibility. Octopi use jet propulsion to shoot through the water at high speeds, they do this by expelling a jet of water from their body. This would explain the Chestbursters flapping tail and the hasty speed of its movement.

Spring - Some may also have noticed that when settled within Kane's open chest the Chestburster's tail seems semi-coiled. I personally have always imagined that to expel itself fully from a body of a host that a Chestburster coils its tail and springs out of the victims chest.

My suggestion would be that the Chestburster in Alien coiled its tail tightly before springing out of Kane's chest assisted with a sharp expelling of air from its abdomen.

In all other instances though I have always imagined Chestbursters as crawling using their forearms with a bit of side-to-side undulation, only using their tails and jet propulsion when requiring speed or to jump. 

@Charza "squirt propulsion" hahahaha that got me

Gross but highly amusing guys!

I think it does not matter so much as its Sci-Fi and sometimes when you scrutinize Sci-Fi you will get flaws in the Science.

The design may not be viable as a real life Organism apart from something that would move slow..

But this is a Alien and it may have super strong muscles etc that enable it to move with speed, that you would not associate with the design.

But then we can use Spidermans Powers, to the same conclusion that his Muscles are super human compared to his body design.

@Gavin Singleton

Excellent points made! 

@Charza

Brings up quite an image! 

@Durp004

Ah, that's interesting, blood traction! 

@Aorta

Music to my ears!

Hahahaha.....you know, bodily function propelled movement would be very much in keeping with the Gigerverse!

@Necronom 4

Nicely illustrated! Ha!