Summary:
Sniffer can't get into minecart. Since all mobs except the Wither, Ender Dragon, Iron Golem, and Warden can enter minecarts on their own, sniffers should also be able to do so.

Steps to reproduce:

1. Summon a sniffer.
2. Summon a minecart nearby.
3. Push the minecart into the sniffer.

Observed results:
Sniffer doesn't want to enter the minecart.

Expected results:
The sniffer will enter the minecart.