Weird trail on algae?

[Burger Wife]

Hi, today I found this strange trail in the algae on the aquarium glass. (I left it there as I am planning to get some otocinclus catfish and want them to have something to eat.) What could have made these trails? Is it harmful?

 

[Fresh2o]

Most likely some type of mollusk (snail, FW limpet). Not harmful.

 

[TMaier]

Most likely some type of mollusk (snail, FW limpet). Not harmful.

And it was stupid staggering drunk by the looks of that line. [emoji3]

 

[Fresh2o]

And it was stupid staggering drunk by the looks of that line. [emoji3]

Haha! Grazing under the influence.
Actually, when MTS (and possibly other snails) feed, they do this side to side thing.