This must have been asked before but I can't find an answer.

SCENARIO:  It takes ten minutes to add a new block of data to the blockchain.  Larry has one bitcoin.  He goes to the mall and within one ten minute period between blocks:

1) Larry spends most of his bitcoin at a computer store.
2) Larry runs next door to a jewelry store, where he again spends most of his bitcoin.

Obviously this can't happen.  What is the mechanism that prevents double spending within the ten minutes between blocks?

Thanks.