Maybe they (the Gars) just want to "play" with the cat.
I have a Green Terror who seems to really get riled up at my cats. (and my grandson) He has lifted the tops, and pushed them kitty wampus a few times now.
Is your cat/cats often on top of the tank? (Like mine)
if i catch the cat on my tank it will get fed to the fish! i have seen it on top of our 13" rhoms tank...one day i should leave the lid off and watch the cat jump up! j/k! our cat's awesome!
j/k! our cat's awesome!