Crocs are very interesting creatures.....know this is off the original posters topic but didn't think it was worthy of its own thread.

just found out the other day that crocodiles increase their density by swallowing stones. (Remember density=mass/volume) 4-5 kg of stones have been found in the front stomach of large crocs. The increased density allows crocs to swim lower in the water and expose less of themselves to potential prey.

The stones also aid in digestion....since crocs don't really chew their food!