The sanguchito begins as a back ocho. The zigzagging motion is interrupted by the leader placing his right foot against the left foot of the follower. Then the leader puts his left foot against the follower's left foot: the left foot of the follower is 'sandwiched' between the left and right foot of the leader. Hence the name of this figure. Subsequently the leader takes a step back providing an opportunity for the lady to enrich the sanguchito figure with embellishments. A forward ocho finalizes this figure. The next video shows how to do the sandwich.
The sandwich which the leader initiates by putting his right foot against the left foot of the follower, is the most common one. Minor changes may prove to be quite surprising. For example: leader's right foot against the left foot of the follower, leader's left foot (without weight) against the left foot of the follower and then pull out of leader's left foot. Consequently the optional gancho has to be performed around the other leg of the leader. Another example is to begin the sandwich half a back ocho later: leader puts his left foot against the right foot of the follower continued by one of the two options mentioned above.
A possible extension of the most common sandwich: leader's left foot takes a step in the direction of right foot of the follower and then the leader moves her free leg with a barrida to her supporting leg. The lady will end up in a cross step which is part of the 8 count basic step.
What is a barrida?
In a barrida, it looks like the man is pushing or dragging the lady's foot with his own.
Still it's a led movement like any other in Argentine tango. The foot is only ornamenting the move.
As a leader you have to lead the lady to step where you want her to go, using your entire body (tango as usual). Rest the edge of your free foot lightly against hers as you lead her. Shadow her foot without pushing it, and you have created the illusion you've dragged her foot.
As a follower you keep your foot in contact with his. You may exert slight pressure on his foot if you would like to return a barrida (also known as 'el arrastre') and appear to drag his foot to a new position. If you are dancing with a sensitive leader, he will match your invitation with a lead for you to step where you are suggesting.
What is a gancho?
During a tango dance step, the thigh of the follower makes contact with the leg of the leader. This contact means that the leader invites the lady to continue her step in the direction of his leg which is blocking the way. The follower reaches her leg in that direction and the point of contact functions as a hinge to swing up her leg. The clip (gancho after a sandwich) demonstrates the leader giving the lady a small push backwards supporting her gancho. When you have gained some control over the gancho you can vary with the intensity and timing of this somewhat intimate tango move.
On the other side a leader may 'hook' his dance partner with a Gancho as well. Just watch this last video and you will see how it works.