It sounds a bit odd. But, I have been noticing that in almost all of the pleasure trips I have made in recent past, I have received some injuries, albeit minor ones.
As far as I can recall, this has happened. For example the Thattekadu trip from Hornbill Wildlife Club, while I was college; leech wounds, scratches and bruises were found all over my body.
The Srirangapatna trip with a trek to Kali Ghati, returned with itch marks, bruises and hurt toe finger.
Kodachadri,Apsarakonda trip - Lots of bruises, sprained ankle...
Gopalswamy Betta - Bruises and cuts from long grass blades
Venugopalswamy Temple - Bruise over shin bone
And similarly for some more trips, I recall the small injuries because by that time I had started noticing their continuous occurrences. Even one of my friends used to find similar stuff on his body after the trips. Hence, we are aware of it now.
That was the explanation of the phenomenon.
Coming down to what I think of it.
It is mostly occurring due to
a) Me exerting too much on myself during trips
b) Improper and spontaneous movements over tricky terrain
c) I am usually too excited/careless to watch where I am going
But definitely, it has become a sort of practice for me to close the account of any trip by seeing a drop of blood somewhere on my body. It gives supreme satisfaction about the entire journey.