When standing underneath solid blocks with sniffers above you, they give off shadows through the solid blocks, even though there are no holes above you.

The shadow is visible when looking forward, but when looking downwards, the shadow will disappear (and reappear when looking back up).

This only seems to happen with fully grown sniffers. The baby sniffers don't have the issue.

(Sniffer_Looking down/forward.png are from a survival world. Recreated.png is an example in a creative world showing the sniffer compared to a cow.