Yang would feel Sveta try and shift, find different positions to try and hold Yang up.  As a result, she wasn't really paying all that much attention to the movie...about twenty minutes later, she would hear something.  "Uhm, Y-yang?  Sorry to bother you and all that, but could you lean the other way a bit?  It feels like I'm going to get smushed into the couch here in a minute..."  Alright, good news despite being asked to move a little - she was doing it because she was worried she might tip over and then fail to hold Yang up.  That was good, right?  "...I guess I should work out a little more with the arms than I do, huh?"  Here she had thought herself as capable, but Yang was simply...overpowering was not quite the correct word, but Sveta couldn't hold her up forever.  This, of course, would provide its own opportunity for Yang to respond to the request - just how she did, though, would be up to her.