Once when they were young they wrestled pretty hard and Sylvestra ended up with an abscess.
The second one was scary. I used to have an apartment with wood floors, and French doors leading into the bedroom. I usually left them open b/c the window unit A/C was in the living room, and it got pretty hot. One day I closed the French doors. That evening, Mr. and Sylvestra came chasing through the apartment at top speed, and Sylvestra crashed through one of the panes of glass in the door, not expecting it to be closed.
She needed stitches above her eye - thank goodness it didn't cut her eye!
I never closed those doors again.
My neighbors downstairs probably thought I had a herd of miniature horses up there, from the way my cats would go galloping and sliding around on those wood floors!
Forgot about the time I came home & found that Mr. had chipped a fang somehow.
And the time he fell of the mantle and sprained his leg.