These newborn baby monkeys have to learn how to hold on tight when they're hanging out with mum - because their enclosure is over a pool teeming with deadly aligators.
The two sets of twins - marmosets and cotton-top tamarinds - are growing up in Vienna's Sea House marine park where they live above a realistic-looking Amazonian rainforest river packed with 'gators and fish.
Aquarium boss Michael Mitic said:"Both sets of twins were born on the same day and the parents seem to be delighted to have them."
"They are very sure on the feet. Well, we've never had one fall in the pool yet," he laughed.
But keepers have decided not to take too many risks - and have kept piranhas out of the enclosure, which includes tambaqui, arowana, giant gourami, stingrays and redtail catfish.
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