Draw the crabs -
"to perform any action in the front line, deliberate or not, that results in a rapid offensive response from opposing German forces, usually in the form of sniper, machinegun, mortar or artillery fire."
Example - #1
Digger A : "Mate, what did ya do that for? It was nice and quite out here with Gerry snoozing."
Digger B : "I was bored mate. Thought I'd draw the crabs for a bit."
Example - #2
Digger to mate: "Better put that smoke out mate, wouldn't want ya to draw the crabs."