It shouldn't come as much of a surprise that rats gamble, since everything that lives and moves gambles. Getting out of bed in the morning is a gamble that the day and life won't end when a hammer that has slipped out of the hand of a roofer two doors down from the newsagent where you get your paper every morning doesn't land on your cranium as you pass. You bet it won't happen, or you stay in bed and sod the crossword. Foxes gamble when they rummage through your rubbish bin that the local hunt isn't about to come round the corner and tear them to pieces (no one having told them about the recent legislation). The pigeon in my garden gambles that the cat won't sneak up behind it as it hoovers up the spilt seeds under the bird feeder. It knows the cat's around, knows the food's around. Doesn't want to die, wants to eat. Takes a risk, on whatever basis pigeons work these things out. Living things gamble or they stay absolutely still and die of starvation.