CHIRPING GIANTS 163 



remain constantly open in expectation of their victims. These 

 hardly cross the fatal threshold before the mollusc snaps the 

 pincers shut — bang. If instead of a silly fish the pincers have 

 trapped the hand or foot of a careless pearlfisher, he may 

 recommend himself to the mercies of God. It would take a 

 lot of dynamite to force the hinge on that coffer. 



Where were these huge clams then ? We found thousands 

 of them in the Red Sea, but they were of moderate size. The 

 biggest one we tore from the sea-bottom was little over a 

 foot broad. 



The coral shallows at Ras Ilet were throbbing with 

 molluscs (ah, those cowrie shells . . .) and there were many 

 of these clams, one at least on every rock and madrepore. I 

 carried out some experiments. 



I wanted to check especially the claims of the underwater 

 explorer Hans Hass. He has stated that the tridacna of the 

 Red Sea possess an incredible sensitivity for a mollusc and 

 that at a distance of ten yards they will close suddenly at the 

 slightest movement made by a man. I began by making 

 movements with my fins, in the direction of the mollusc, at 

 a distance of only two yards. 



Then I got slowly nearer and placed the blade of my knife 

 between the valves of a big one without actually touching 

 any part of it. The clam did not even twitch so I tried poking 

 it in the flesh. It contracted slightly and the valves closed 

 about half an inch. Finally I plunged the knife between the 

 valves into the body of the clam — the doors closed with a 

 bang. The knife-blade was easy enough to draw out again 

 because of the indentation of the valves. I repeated this 

 experiment with several clams using my fingers. Only one 

 out of twenty actually nipped me and then only when I was 

 over-rough with it. 



Naturally these observations on small tridacna are not 



