Crawl, slither (5)
I believe the answer is:
creep
I believe this is a double definition.
'crawl' is the first definition.
(I know that crawl can be written as creep)
'slither' is the second definition.
(I've seen this in another clue)
(Other definitions for creep that I've seen before include "Walk slowly, silently" , "Move slowly with body close to ground" , "Crawl silently" , "Tiptoe" , "narrow passage" .)