A dialogue with Sarah, aged 3: in which it is shown that if your dad is a chemistry professor, asking "why" can be dangerous.

SARAH: Why?

DAD: Why do the molecules have a hydrophilic head and a hydrophobic tail?

SARAH: Yes.

DAD: Because the C-O bonds in the head are highly polar, and the C-H bonds in the tail are effectively non-polar.

• parenting
• science