bite? at base of tail

[Leenknegt-Lioen]

Hi,
Today I noticed something about Daedalus' tail: he has a little bald place
on the base, and there is a little scab.
Now I can't believe Daedalus and Icarus would be fighting, they are the most
affectionate gerbils I've ever seen. And they groom each other all the time!
Is there something I should put on the wound?
Has anybody any idea about what happened?
Thanks for any input!
Sarah