I was only seventeen and quite gullible I suppose but I didn't think he was yanking my chain at the time.
I don't know who your survival instructor was but he's probably died of septicaemia by now if he's ever used the squeeze and pull technique.
The leech will vomit your blood and its toxic stomach contents back into the wound and give you blood poisoning before you can get it off. It'll also whip round and reattach itself to one of your fingers before you can throw it if you give it half a chance. That was the advice I got from the senior medical officer that accompanied us to the bush in Malaysia for the joint special forces jungle warfare exercise 'elang osprey' in 1997. Oh, how I miss those free adventure holidays I used to go on at her Maj's expense...
Anyway, if you keep a condom in the Sammio survival kit you could always use it as a waterproof dizzy cap cover in the rain though.