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An entrance leads to a room inside the sculpture where visitors can buy sticks of Blockhead rock

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The artist hopes his sculpture looks like a black hole from St Paul's on the other side of the Thames

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Tate Modern visitors can also see how McCarthy developed his ideas in an exhibition of his background work

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One passer-by described the enormous inflatable sculpture as "cartoon-like"

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Blockhead dwarfs passers-by but is dwarfed by surrounding architecture in turn

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Daddies Bighead is based on a ketchup bottle

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McCarthy uses tomato sauce in other works to represent bodily fluids