The Russian's response was too spontaneous, too unexpected to be false.

But neither of them is derived; each is too spontaneous, too fresh from the poet's soul.

He was too spontaneous and liberal with his consideration to seem conscious that he was showing any.

The Countess all but jumped from her chair in her surprise-surprisethat seemed too spontaneous to be feigned.

Being too spontaneous without some basic groundwork might seem like fun, but you could find that minor, practical glitches will soon reverse this impression!