With McDonald's (MCD - Get Report) shares hovering around an all-time high, it's appropriate to reflect a bit. 

In January, McDonald's did something once unthinkable: it gave away its secret sauce in bottles for free.

McDonald's dished out 10,000 bottles of Big Mac special sauce to tie-in with the release of its new Grand Mac and Mac Jr. sandwiches. Each bottle was marked with a number, for you collectors out there. Except for special promotions in Australia, and one very pricey bottle auctioned in the U.K., the sauce had been available solely in the U.S. on the company's waistline-busting signature sandwich.

Our first instinct once getting our hands on a bottle? Why not do the unthinkable: slather Big Mac sauce on competing burgers from Restaurant Brands (QSR - Get Report) Burger King chain, Wendy's (WEN - Get Report) and Shake Shack (SHAK - Get Report) . Suffice it to say, the Big Mac sauce should only be used on a Big Mac.

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