hollow leg syndrome

(Actually happened April 26 2012)

Me: I think someone (indicating Small) is going through a growth spurt; he's got hollow leg syndrome.
Little: what's that mean?
Me: it means he's eating so much that we think his legs might be hollow cuz how else would he fit all the food in?
Little: ooooh.
Me: d'ya think that's what you've got Small?
Small: *shakes head*
Me: no? just a tummy that empties whenever someone opens a door? (something he said earlier on this week)
Small: yep!
Manwife: *grinning* I dunno, what we gonna do with you Small?!
Little: sell him!