I have watched a number of guitarists do a certain technique before where they push on the upper body of the guitar near where they strum. I have seen it done on both on acoustic and on electric guitars, but have yet to figure out exactly what they are doing. I have attached a video clip (first two seconds) where this is being done. Can anyone tell me what this technique is called, and what it accomplishes outside of just bending the strings or using the whammy bar [if anything]?
I looked and could not find a similar question, but I am not a guitar player, so I might be missing the correct terminology.