Agree with all comments but if something is bent or misaligned they are darned difficult and need more than technique to release. Also as springs weaken the bonnets can lift up at the correct speed which is why bonnet straps are added I presume; demonstrating that the catches are far from bomb proof. Until your bonnet/s fly up at speed don't be too complacent about how easy they are to open, unless you have a bonnet strap of course.
