calcium deficit

I met a little kid the other night who likes to make "mmm good" noises when she's eating something yummy. Her mom heard her making really loud lip smacking noises the other day and discovered she's filched some egg shells from the garbage and was crunching away on them. I'm still trying to figure out what she found so tasty about egg shells. Was it something clinging to them from the garbage or the crunchiness or do egg shells have some wonderful flavor only detectable to those under the age of 2?