But comets, thanks to their eccentric and frequently long orbits, are trickier to study up close.
One thing is certain: the situation is trickier for David Miliband than it was before his brother entered the race.
In the America of 2013, rejecting students on the basis of their not happening to be brown is ever trickier to defend.
But as we grow older, finding women to look up to becomes, like everything else, a trickier minefield to navigate.
It may be a trickier dance in a primary in which the most partisan Democrats are often the only ones who show up at the polls.
And Trigger was a trickier monkey than most that way, when she felt like it.
The Rebs weren't as good as we were, but they were trickier, and they could fight.
Esau could never see that there was any important difference between himself and Jacobexcept that his brother was trickier.
There were newer models and trickier weapons, but none which worked so smoothly under the touch of Andy.
She was fleeter than Gerda, she struck harder than Kay, she was trickier than all of them, the beloved girl.