Jason on....gravity

As I was cleaning up after dinner tonight, I heard a snippet of a conversation in the play room between Jason and Alanna.  They were "discussing" the concept of gravity.  How this conversation started, I do not know.  I heard Jason say something about "it's a force that makes you stay on the ground"  and "it makes things fall."  A minute or so passed, and then Alanna came to me to ask me what "gravity" is; I promptly punted this back to Jason.  I choose my topics of discussion, especially at the end of the day, carefully.  This would lead to a multitude of questions I wasn't up to tackling.  So she went back to Jason to try to decipher what this mysterious "gravity" thing is.  I don't really know what they talked about, but she happened to drop her Hello Kitty phone.  Then she looked at Jason and said "I don't like it when gravity makes my phone fall." 

She also announced at the end of dinner that she had a "bum cold."

We have yet to figure out what that means.  Any ideas?