The exact mechanism of its action is not yet known.

The exact mechanism of these effects is not yet known.

However, in many cases, the exact mechanism of killing is not known.

The major mechanisms known or hypothesized are described in turn below.

However, a specific neural mechanism for this is not yet known.

The former mechanism is well known while the latter still needs exploring.

But the exact mechanism of its functioning is not known to all.

The molecular mechanism behind this model is not fully known.

Though the mechanism is known to affect materials without these physical observations.

The "hole" could not be fully explained by any mechanism then known.