It sounds like he was wanting to mate with her. Males will often vibrate their tails and then begin biting the female along the tail and/or back and eventually the neck before mating. Either that or he was just being aggressive.

Are you wanting to breed them? Are they the proper age/weight to breed? Are you ready to breed them? If not, you should not house a male and a female together.

Also, even if you do plan on breeding them, they should both be adults before you house them together since they are male and female. You don't want to endanger one of them if they are too small. Also, you don't want the larger of the two dominating the other one.