Common knowledge

Are there things that we assume everyone knows? Knowledge that all of us have picked up somewhere along the way. I have realised in the last little while that there are two pieces of this knowledge that had escaped me.
The first is about canaries. When discussing a colleague who had been gassed and robbed while staying at a hotel, the conversation turned to methods of gas detection. Specifically, we talked about canaries and how they had been taken down into mines. The miners knew dangerous gas was about when the canary fell off the perch. We all know that. But what I didn't know was that the canary died. It didn't regain consciousness. There was no happy flapping of wings; no jumping back up on the perch; no chance to save mankind again ... just miners looking for a replacement canary.
The second tidbit of universal knowledge to escape me was about whales. On The Simpsons last night, Grandpa Simpson drove his car into an aquarium and as the water escaped, it left a whale crumpled and gasping on the car bonnet. But why would the whale be gasping (forget for a moment that we're discussing an animated sit-com) ... because whales breathe air. So I mentioned this to a friend at lunch today and she gave me the "everyone knows that" look. And then when she realised I didn't (know), she gave me a short lesson in physics - out of the water, whales are unable to withstand the pressure, and gravity has its way. I guess that's the same as saying their weight crushes their chest (?) and they suffocate even though they have air to breathe. That's why there's such a rush to get them back into the water.
I'm hoping there are also known answers to some of my other questions:
• Why do Crime Scene Investigators do everything by torchlight?
• Why do sandwiches taste differently depending on how they are cut?
• Do you continue to tan after you're dead?