I have small but very strong magnets for my fridge, and they will stick to nails/screws in drywall. Easy and non-electronic way to find studs.

Humans live in social groups. Humans are also great at fighting. On top of this, humans (like other animals) have an instinct to protect and care for their young. So, given this level of protection, if a baby has a need (food, hot/cold, needs care) it is much better for a baby to loudly communicate this to nearby adults so it survives infancy, because the adults can almost always handle external threats that might arise.

Not quite. I know this isn't ELI5, but basically if the WBCs are policemen, the selectins (and others) on/near the vessel wall are going, "Hey, my friend is in trouble! This way!" and pulling on their shirt sleeves. Once it exits the vessel, they can follow concentration gradients.