Slimy creature strides purposefully over and forces person to come with them (11)

I believe the answer is:

frogmarches

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'slimy creature strides' is the definition.
The answer and definition can be both to do with motion as well as being verbs in their -s form.
Perhaps there's a link between them I don't understand?

I don't understand the remainder of the clue.

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I've seen this clue in The Irish Times.

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