What's blood?

Recently, my wife and I noticed a little blood on our daughter's clothes.

"Sammy, you've got blood on your clothes!"

"What's blood?" she asked.

Uh, good question. Hard question. How do explain blood to a three-year-old?

"It's the liquid inside your body, honey."

"Oh." She thought about that for a minute. "Why?"

"Well, blood goes all around your body, delivering oxygen to your fingers, your toes, your eyes and ears," I answered, as if that would clarify things. She looked at me.

"Put your hand on your chest, like this," I said, as I placed my palm over my heart.

"I don't want to!" she said.

"It's okay, I just want you to feel your heart. You'll feel it pumping your blood around your body."

"Okay, daddy." She touched her chest. "I want to play a differnet game now."