you do have the cage covered right? ok to keep door area opened to room. if you have put a box in the back tilted on it's side with no flaps only about a third of the length of cage, it gives him a place to huddle while you change food, water, and litter. (take out things, shut door and return them by opening door only leaving enough room for what you need! My feral kitten went flying like a flying squirrel when I opened the door the other day and if she hadn't aimed for the hinged end (silly girl) she would have made it out!).
I read to my ferals. In a voice like I'm reading to a kid. Just whatever I happen to be reading at the time. They relax, start walking around the cage while I read, even fall asleep! (As opposed to staring wide-eyed at me with fear!) I make occassional eye contact then look away. (like we're supposed to do with ferals anyway- also, look at them in the eyes, close your eyes for several seconds, then open them looking in another direction. do this a few times, and you'll see them start to do long eye closes and looking away- it's a sign of trust. When you smile, don't let your teeth show.)
I've been petting my feral with a back scratcher. she hisses but when she finally stops, I switch to my hand, she hisses again but eventually stops. this has been going on 5 days. Still hisses when i initially approach her- sigh....
takes a lot of patience.
Is there a rush on getting to the vet?