Why a box and a mouth are both 'light' in Japanese

Where the picture shows up in 軽い

1. 1

   the arm rises

   この箱は軽いので一人で運べます。

   kono hako wa karui node hitori de hakobe-masu

   This box is light, so I can carry it alone.

   Hands grip the box handles and the arms come up with no resistance

2. 2

   the body doesn't drag

   今日は体が軽いです。

   kyō wa karada ga karui desu

   My body feels light today.

   Feet taking the stairs two steps at a time first thing in the morning

3. 3

   only a shallow degree

   軽いけがで済みました。

   karui kega de sumi-mashita

   It was only a light injury.

   One bandage goes on and the person walks straight back to work

4. 4

   a small meal

   昼は軽く食べます。

   hiru wa karuku tabe-masu

   I eat light at lunch.

   One rice ball and a cup of tea on the desk, nothing else

   軽く食べる means eating a small, quick amount — not eating something light in texture.

5. 5

   a mouth that leaks

   口が軽い人には話せません。

   kuchi ga karui hito ni wa hanase-masen

   You can't tell anything to someone with a light mouth.

   What you said flows out of his mouth and straight into the next person's ear