One of the most popular dances, a classic you are likely to meet at every festival. It has a gallop, a strip the willow and a sort of shunting back and forth to get from one end of the set to the other.
Longways sets of four couples... So you need a partner⬀ and you join up with 3 other couples. Men on one side, ladies on the other. It's good to make sure that you know where your set 'starts' and 'stops' (and, once you've got four couples, make sure any further couples don't attach themselves to 'your' set).
As the result of a strange construct of geometry, the men will find they have more time when Stripping the Willow in the Foula Reel than in, say, Stoke Golding. This is because the working couple⬀ are stripping up⬀ the set.
There's an easy way and a difficult way of doing this. The difficult way is swing your partner when you get back to the top, untangle yourselves, make an arch and get the lady to the outside of the set, facing down, looking over the heads of the line of men.
The easy way is that the lady carries on with her left arm turn with the last man. That is keep that last turn of the Strip the Willow going, until she is facing down the outside of the set and launches herself down behind the line of men. Her partner just has to stay out the way, make it clear and obvious that the lady needs to make the most of the left hand turn and join in with the arch when she's heading down the set.
Listen out for ... First man push, other men pull
If you are going to pull:
Hold your hands to beckon your partner to follow you.
You don't have to step together to join hands only then to step back. Hold back and let your partner come to you.
If you are going to push:
Come into the move with your hands showing that you would like to push.
A Poussette⬀ is where the top couple gets to the bottom of the set with a shuffle forward and back while everyone else does a shuffle back and forward...
The common way it is described is to say "take two hands with your partner" and then telling the top man what to do...
The top couple do have to make sure they have got to the bottom and out the way by the end of the music. If they are not careful, the new top couple will run into them as they gallop down.
Poussettes can be messy; people forget whether they should be pushing or pulling, people crash into each other, they can get out of time with the music and the first couple has cut and run for the bottom to get out the way.
A Shetlands dance, supposedly from the Swedish Väva Vadmal, or the 'Norwegian Country Dance' (The fiddler's companion, quoting Traditional Dancing in Scotland, Flett and Flett, 1964).
Väva Vadmal in the Swedish Wikipedia
Youtube shows quite a number of local variations of Väva Vadmal, which include moves which are quite recognisable - there are dip and dives, forms of strip the willow and thread the needle, arching down over the women and up over the men, and poussettes (variously in the Väva Vadmal från Väckelsång, Rönnenberga, Jät)
... an old lady of 84 who tells me she was paid sixpence an hour as an extra at the cliff scene, and to dance the Foula Reel
for Michael Powell's 1936 film, The Edge of the World.
It may look a bit different north of the border. The Scottish Country Dance Book, Book 4, 1927 (see the Strathspey description) has the first couple dance down and back and Strip the Willow from the top.
There is a second variation  which drops the gallop down and double Strip the Willow back, replacing them with a single Strip down and back, a bit reminiscent of the Drops of Brandy
If feels awkward to arch over the sides, get back to place and then change direction for the Poussette, then there's a variation that flows better. The caller will say:
The working couple, who have been arching up over the Ladies' line, get back to the top and flow into the Poussette, no change of direction required.