Do any of your cats bite?
Ours does - I think she is just playing as she only seems to "hold on" rather than really sink her teeth in (unless you try and pull away!). She usually does it when you are stroking her calmly and quietly - she'll suddenly just go for it.
She is a keen (indoor) huntress now, as evidenced when playing with her so I wonder if the two are related? She is also a very independent madam, although mellowing a little now.
Despite owning and caring for numerous cats over the years, I've never had this before!