Liam funny!

Well as a mom of two growing boys, what can she say to a comment like this!
I crouched down to help Liam put his boots on, and all of a sudden he says "Mommy that's a tunnel, see right there, that is a tunnel." He then proceeded to show me the tunnel, and demonstrate his hand going into the tunnel. Can anyone give a guess what that tunnel was?

Oh that Liam of mine!