What do frogs, flowers, and tacos have in common?
They're all a little magnetic. In fact, at the atomic level, everything is a little magnetic, even you.
This is because the electrons in every atom have a property called spin that makes them behave like tiny magnets, each with a north and south pole.
Why don't you attract things like iron nails?
Well, this is because you aren't what is known as a permanent magnet. In a permanent magnets, the spins on neighboring electrons all naturally point in the same direction. That is, their poles line up.
In most materials, however, the electrons pair up so that they cancel out each other's magnetic pull. These materials are still magnetic, but they're about a million times weaker than the average refrigerator magnet.
Though the pull is weak, scientists have been able to levitate frogs using the weak magnetism in their bodies.
When an object is exposed to a permanent magnet, it's either attracted to or repulsed by the magnet depending on how the object's electrons line up. For iron nails, the electrons line up so that they're attracted to the magnet, but for frogs and humans, the electrons line up so that they're repulsed. Usually, this repulsion is so weak it isn't noticeable. However, when you're dealing with a really strong magnet, it becomes a force to be reckoned with.