Does this happen at your house?  I have been stumbling over these large pairs of socks lately. The most recent find felt exceptionally dense.  Upon examination it turned out to be several pairs of socks wadding together. Some clean and some, um, less so.  

me:  So what's with the wadded up socks?

them:  It's a sock football.

me:  Why?

them:  To play football with (falls under 'ask a stupid question…') 

me:  But you have a football.

them:  Yeah but we can't throw it in the house.

Ah.   That explains it.   Resourceful – if barefoot.  : )