Check out the excellent reasonable doubt analogy below from The Burden of Reasonable Doubt: When a Standard Designed to Protect Defendants Actually Hurts Them by Jim McElhaney:
“Is it possible for the government to prove guilt beyond a reasonable doubt just on circumstantial evidence, without any eyewitness testimony? said de Manio.
Of course. Take a simple example. Suppose that you take a mouse and put him in a box. Now take a cat and put him in the box with the mouse. Then take the lid and cover the box. Now tie up the box with string so the lid can’t come off.
Leave the room for half an hour. When you come back, untie the string, take off the lid and look inside. There is no mouse, but there is one happy cat.
Do you know what happened? You weren’t there, there are no eyewitnesses. All you have is circumstantial evidence. But you know beyond any reasonable doubt what happened to that mouse.
Let’s do it again. Put the mouse in the box. Put the cat in the box with the mouse. Put on the lid. Tie it down. Leave the room for half an hour. Come back into the room. Untie the string. Take off the lid and look inside.
There is the cat. No mouse.
But look—back there in the corner of the box. There is a hole, just big enough for a mouse.
That hole is a reasonable doubt. Now let’s look at the holes in the prosecution’s case.”