I figure to break up the monotony of me not sharing many of my glitches, here's a "new" glitch (well, new for you, old for me) which I will give a full disclosure.
Of course, this means the glitch is practically useless.
But it's still fun to see it in action.
In this case, the reason it's so useless is, it turns out the glitch is incredibly specific to the version of lemmings you have. And even when it works, the effect is more hilarious than useful.
Forget about the Mac and SNES versions etc., in fact, even amongst the DOS versions, it only works on the "original" DOS Lemmings (the one from abandonia.com works too). Not only does it fail on ONML, but if you use the so-called "CD" DOS version where they corrected the music (so that when you restart a level it doesn't go back to the level 1 music), you won't get the glitch either. I've also tried Holiday Lemmings '94 and the glitch doesn't work there either. Feel free to check out the other versions as well.
Most importantly, it doesn't work in CustLemm and its derivatives that I made (CustLem2, Nocdlem, etc.), which truly seals its fate as a useless glitch.
So, the glitch:
When a non-climber builder finishes building and does its shrug, if you assign it a climber while it's shrugging, it will abort the shrug immediately and start walking. Except it will be doing the shrugging animation while walking, until it is converted to some other action (ie. jumping, falling, or a skill you assign).
The only possible use is to gain that small fraction of time during which the lemming is shrugging (and therefore normally not moving forward). Adding the restriction that it doesn't work in CustLemm, the usefulness of this glitch would be rather limited, except maybe for Timballisto.
However, it is quite funny to watch. It's hard to maintain the glitch state because as soon as the walker falls a little (3 or more pixels) or jumps (a step of 3 or more pixels), it will revert back to the normal walker animation. However, it turns out Fun 19 is the perfect place to see the glitch due to the terrain: let lemming #1 build somewhere left of the cusp between rainbow arches #1 and #2 (counting from left to right). If you build at the right place, it's possible to build a full bridge without turning around, and have the bridge touches the raising slope of arch #2. You might also want to make lemming #2 block to divert the crowd away from the builder.
Now apply the glitch by assigning the climber when the builder finishes and starts shrugging. Watch as he glides along the long rainbow pathway shrugging over and over!