As it relates to Phantom Shifts:
Many others have described the sensation of being "shifted" or "feeling shifty" when around other therians. The effects of such do not trigger in all therians. Many therians who do not experience shifts, more often then not, do not react to a Group Shift.
This can either be a suggested stimuli, a subtle psychological response, or an automatic instinctual response.
The effects can elicit different emotional responses from those who experience a Group Shift.
A discussion of wings, their symbology, species differences between the anatomy of wings and the like create a subtle Psychological response. Those discussing the subject of wings feel, either in whole or in part, a shift of perception and sensation to that of /having/ their own wings.
A group sit around discussing different forms of shifts, of which Phantom shifts may or may not arise. Those involved, actively reach out for their phantom limbs, for the feel of them. Some may be able to "summon" them up, while others react to the subtle psychological response.
A group meet for the first time, or may be sitting around talking of topics not involving therianthropy, and experience a phantom shift. This may or may not trigger others to feel the same shift without realizing that the others are also responding.