Ubiquitin, you’re correct that those could be tzaar baalei chaim (I don’t know to what extent that happens. Several people have commented that they have not observed any cruelty, but I don’t think it never goes on).
I was responding to Flatbusher’s comment, “Without going inside a chicken’s head, how can anyone know whether the chicken has tzaar or not from the process of kapporos?”.
Tzaar baalei chaim is not about guessing what might be going through a chicken’s head.