Jen, I believe that Lily has already learnt now how to open it, she has tried it again. I wonder if it is possible to replace that one by one of these "round" door knobs you have to turn around (sorry, don't know how to describe that better), and I wonder if my landlords would let me (they have hardly tolerated the cats anyway).
If not, I must never forget to turn around the key from now on!!!

Kirsten