Yes, basically a bolt is a big, thick high-current conductor, passing through the center of the toriod.
If you think of a 1,000 turn 110V primary as being a conductor that passes through the center of the toroid 1,000 times, and a 100 turn 11V secondary as being a conductor that passes through the toroid 100 times, that's a reasonable analogy (numbers pulled out of the ether solely for the sake of example, but not totally out of scale with reality).
Now, no current flows in the secondary until you close the circuit between the two ends of the secondary conductor. -Open circuit secondary draws no current, and no power is drawn from the primary (other than essentially insignificant core losses).
Now, 1Amp drawn through our 110V primary will equate to a 10Amp current in the secondary. (W=IV, power is unchanged, so of volts go down, current goes up and vice-versa.)
So consider our 1-turn conductor. (The bolt.) -As long as nothing which passes outside of the toroid's core connects the two ends of the bolt to each other electrically, no current flows. As soon as you short them together, you have a turns ratio of 1000:1 (1,000 turn primary, 1 turn secondary). Since the secondary is shorted, it tries to pass as much current as it can and things get pretty nasty. Don't be calmed by the fact that a 1000:1 turns ratio gives you 0.11Volts from a 110Volt input... 1 amp flowing in the primary will give you 1,000 Amps flowing through the secondary bolt!
A thousand amps. Think about that... it's enough to weld with. And welding is exactly what can happen.
In reality, if you short a secondary, the instantaneous current flow is WAY larger than what the transformer was designed for, and the core saturates, wire burns and all sorts of nastiness breaks loose... basically be VERY careful with toroids. If possible, use a plastic cap on the top of the bolt: -if the conductive tip of the bolt touches the top of a conductive metal case, the same thing happens. -I like to use those plastic "rod-caps" on my toroid bolts for exactly this reason.
Keith