local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
while true do
if mouse.Target == script.Parent.Parent.Parent then
print("Mouse hovering over food")
script.Parent.BillboardGui.Enabled = true
else
script.Parent.BillboardGui.Enabled = false
end
wait(.1)
end
It is a local script and it shows bill board gui when shown on mouse contact, you know what to do ;)

2 comments
Could you try printing mouse.Target in the loop to see what your mouse is targeting when you're trying to target the food? This can help identify the problem.
Roblox says Target is nil to mouse apperently.