I have noticed this before but today I opened a can of tomato soup for the poorly DC and in a flash our two cats were around my ankles expecting dinner. The thing is, they have never ever been fed canned food so it's not like they hear a can popping open and expect Whiskas to be served out of it.
My cat can smell chicken from the bottom of the garden!! He had just gone out yesterday morning and I was making my DS packed lunch...leftover chicken on rolls...the cat was back in a flash sitting on window sill meowing for attention!! DS ended up handfeeding the cat slivers of chicken to pacify him...whilst the dog waited waited patiently for any crumbs to be dropped.
Our cat and dog work as a team...the cat will spot something left on a plate on the worktop, he pushes large pieces over the edge to the waiting dog and then finishes off the crumbs on the plate. Has to be seen to be believed. They also do this with the plastic milk carton lids that I have washed for recycling...the cat manages to get the lid free from the draining board and knocks it onto the floor. Dog and cat then play chase round the floor trying to catch the lid!