A very interesting song to study, specifically the version being played by professor Toro. We start off with the chords E7 and A Major for the introduction followed by adding in the D Major chord. Essentially the repetition takes place within the E7 and A chord giving it a wonderful swing to the song.
The main variation made use of to give it the swing is by adding the F# note to the E7 chord. This is done by playing the 4th fret of the D string with the ring finger. The chords played are as follows:
E7
2.0.2.0
A Major
0.2.3.2
D Major
0.0.0.3
A typical progression with these chords would be like the following:
0.2.3.2 0.0.0.3 2.0.2.0
The second part of the song makes use of the C Major chord and then slides it into the second position of D Major. We then climb up into the first positions of the chords again by playing a single bar on the third fret, followed by a bar on the second fret where it is then possible to carry on with the E7 chord by adding the middle finger to the third fret of the B string and continue to jam the song in the same progression.
C Major
3.2.1.1
