Bella is a 20 pound JRT mix. Not TOO high energy for a JRT (I've had several), and very sweet and loving and affectionate. Sleeps with me and cuddles beautifully. She is four years old, was rescued at 3-4 months, and has become increasingly aggressive towards my 11 year-old Yorkie -- goes for the jugular and has caused plenty of physical damage which has gotten worse and worse. I have, honestly, never had a sweeter or more loving dog, but she came with some trust issues and simply has moments where she attacks the other dog (doorbell rings and they both run to the door barking -- she turns on him; in kitchen together while food prepared and he gets too close -- she turns on him; if he is next to me and she approaches and he growls at her -- she attacks). She doesn't bite people, but she barks like crazy (while wagging her tail the whole time) for 2 full minutes when a new person enters the house, then she is all over them for love and affection. I have worked with a behaviorist, try keeping them apart in times of increased stress (like the instances above), but the attacks have become more frequent and unpredictable. This is breaking my heart, but I cannot let the Yorkie continue to be injured and possibly killed. SHE MUST BE THE ONLY DOG IN A HOME WITH NO CHILDREN (she has never attacked, but I think the increased aggression must be heeded in this regard).