Here's that first one you mentioned in gif form
[IMG]http://gifsoup.com/view2/1418837/taeyeon-shocked-o.gif[IMG]
She's actually pretending to be shocked hehe, it's from a show called Horror Movie Factory where they were being taught how to act, mostly focused on horror movie acting.
I had another one that showed her smiling just after but I can't find it
Here's another one from HMF
[IMG]http://media.tumblr.com/tumblr_mamljmvBGd1rng4c6.gif[IMG]
She's being punked! They went into a haunted house that was really just a resort lodge during the night hehe, yuri was being possessed and the 'expert' they had kept telling her to do things (like the above) to unpossess her