The Bug:

Sniffers will sometimes try to sniff out and dig in blocks they cannot physically reach, resulting in them giving up and being unable to find seeds.

This most often happens with blocks such as fences, where the block is technically not fully unobstructed but the Sniffer can't physically reach it to dig out seeds.

This behavior is clearly demonstrated in this video below:
SnifferFence.mp4

Steps to Reproduce:

1. Enclose a Sniffer in a a fenced in pen with grass in and outside of the pen
2. Wait for it to start Sniffing. Sometimes it will dig within the pen
3. However, other times take note that it will try to sniff out one of the blocked covered by fence, with it being unable to do so