ok, so i see that this thread is quite old, and might not be of much interest to anyone but myself... i have a small flock, broken into two groups, 1 cockerel has 4 pullets, and the other cockerel has 3 pullets, for a total of 9 birds. i've had them since they were two days old, and they have experienced daily handling, and are now 9 weeks of age. maybe they are all still technically chicks... but the males have been "crowing" for 5 weeks already, and now produce a true recognizable crow. now, to the point...
my most trusting pullet, wilma, a barred rock was the first to display a peculiar behavior during handling. she was about a month old and she lifted her wings so i could get my fingers underneath... and then she lifted her tail, and puffed up every single feather on her body and started chirping and cooing. all the rest of the birds came to investigate, and just stared at the scene... as time progressed, i have achieved the same response from every bird, including the cockerels, which confused me as i really thought it was a female sexual response...regardless of age, surely it felt nice to be massaged and scratched gently and have the feathers smoothed.
my flock is actually part of a larger group that i rescued from certain death due a shipping error that landed them hundreds of miles from their intended destination. i kept 9 of the original 26 chicks, and was super fortunate to find awesome homes for all of the rest. all are thriving

so, whatever it is that i'm doing... tickling, stimulating, i enjoy the connection, and they clearly enjoy the sensation... so yeah... I say Tickle A Chicken!