I think your negative sample set is a little biased. Since all the phrases start with verbs like "was in the car" or "went to the park", these kinds of phrases are given lower probabilities.

For example:

    > twss.prob("was on a stiff pole");
    0.016050826334564946

Only 1.6% chance of that's what she said?!?

EDIT: Counter example:

    > twss.prob("that's one stiff pole");
    0.9767718880285885