When someone sidles, they move sideways in a sneaky or cautious way, especially because they don't want to be noticed.
Sidling can be seen as a little sneaky or suspicious, like when someone is trying to avoid being seen or caught doing something.
Examples:
The cat sidles up to the bird, trying to catch it.
He sidles over to the cookie jar, hoping no one sees him.
She sidles away from the teacher, not wanting to be called on.
The raccoon sidles around the garbage can, looking for food.
The spy sidles past the guards, trying to get into the building.
The ghost sidles through the walls, scaring everyone.