We lock my cat Ginny out at night so she doesn't bring in the results of her hunting- although we let her stay in the kitchen in winter. She has now worked out that if she headbutts the catflap enough times and with enough force (I'm not joking here!) then the little latch that holds it in place will pop out, she can shove against the catflap, the entirety of the lock will come out and she can get in. Why? So she can wake us up. She thinks it makes us feed her faster too...sadly, to get her to shut up, she ends up being right. I really need to buy a new, more secure catflap. At least now I can can explain why not when someone tells me cats are stupid...