My Woodhouse's toads all do this, many times without apparently looking at the prey item. As soon as it moves though, the prey is grabbed. I've always been curious what prey item actually responds to this. The usual domestic fare (Dubia, crickets, etc.) certainly don't - in fact, the roaches usually freeze if anything moves near them, and the movement is too subtle to scare a prey item into moving IMHO. It seems to me that a predatory insect/animal might be the best guess - I could see it attracting smaller frogs/toads, for example...